A sexually transmitted disease breaks out and affects several members of the hospital staff. Chief Webber promptly calls a meeting. Meanwhile, the chief reluctantly tells Dr. Derek Shepherd about his own medical concerns. Izzie and Cristina worry about a patient's wife and daughter who can't agree on his care. Burke treats his college buddy Bill, whose medical diagnosis raises some questions regarding his wife's actions. Then just as Meredith and Derek grow more intimate, a surprise is revealed.

Picks up where the last episode left off. Meredith attempts to work with Addison Shepard. George is pimped out to relay the hospital gossip back to Webber. Meredith and Cristina relate at Emerald City Bar about what dating their respective attendings is like. Cristina ponders her relationship with Burke while trying to make a decision. Meredith is devastated by the latest blow to her love life. Meanwhile, Joe the bartender collapses.

There's tension between Meredith and Addison. We find out why Derek and Addison aren't together. Bailey puts George on an impossible case. The rest of the interns operate on a family that was just in a car accident.

Cristina and Meredith try to figure out if Cristina should tell Burke that she's pregnant right before Cristina faces an emergency. Alex and Izzie get closer while Meredith's mother gets too close.

As Cristina tries to recover, she proves to be a very difficult patient, and a visit from her mother doesn't improve her demeanor any. And Meredith's mother, Dr. Ellis Grey, has the hospital staff running in circles.

Cristina goes right back to working right after being discharged. Izzie isn't talking to Alex. Derek and Meredith treat a patient. George and Alex get stuck in an elevator.

Train Wreck victims come to Seattle Grace and all staff gets called in. Everyone deals with really weird cases. Except Addison and Izzie. They work with a woman who is pregnant.

Cristina, Izzie and Meredith take care of Shane, a man who appears to be crazy and claims that he is pregnant. Shane's case induces a spreading fascination among the staff. George relates to a patient's husband.

Meredith tries to avoid the Shepherds. Cristina and Burke go out on a date and end up getting caught up in their jobs. Derek asks Meredith not to ignore him until Addison comes walking around the corner.

It's Thanksgiving at Seattle Grace Hospital but the holiday's festivites are less than in order. Meredith and Derek try to counsel a family after their relative has had a seriously traumatic accident.

Dorie Russell is waiting for quintuplets, all 5 girls. Her husband seems more concerned than she is but she is set to bring her babies to their term of 36 weeks. All the departments are on call for the quintuplets as three of them have developped problems of different kinds. Meredith last night's stand shows up at the hospital with priapism and they need to call Derek Sheperd for a consult which puts Meredith in a very embarassing position. Alex and Derek must take care of a patient who has a tumor inducing thirst as a side effect. On the love side, Alex and Izzie are having some slight sexual problems, while Meredith goes on adding one night stands and Cristina is thrown off course by being "keyed."

Cristina Yang has little sympathy for Constance Ferguson (special guest star Rosanna Arquette), a prison inmate who jeopardizes her health just to get out of solitary confinement. Meanwhile the interns all keep careful watch on the family of premature quintuplets with a variety of serious health challenges, Izzie's anger at Alex reaches boiling point, and Dr. Addison Shepherd decides to teach Izzie a very painful lesson.

The holiday season has started but not everyone is in a festive mood. This is Alex's last day in the hospital unless he passes his boards practical exam the next day, thus everyone helps him to review so that he succeeds. However, Izzie is not happy about the others helping him and Meredith has to remind her of the true spirit of the Christmas holiday. Justin is in need of a new heart. One is available but he does not want it because he does not believe Santa gave it to him as his mother said. Cristina and Burke, both handling Justin's case, have opposing views on the matter due to their different stances on religion. Despite a reconciliation with his wife, Derek isn't in a festive mood. George has a simple case of a woman who has a bleeding ulcer, he realizes that the ulcer is caused by her entourage but fails to keep them away, with the consequence that it perforates.

Cristina is bothered by a new year's mandatory work limit. Izzie patient, Denny Duquette, wants two things: 1. a heart transplant, 2. Izzie. Addison detests Derek's trailer, Derek visits Meredith's mom, George treats a young teen hermaphrodite frustrated by her pre-pubescence. Other news includes patients doing uncanny things and relationship havoc being wrecked between the doctors, as per usual.

Meredith and Cristina lie to each other and themselves about their relationships with McDreamy and Burke, respectively. George is given a hard task to expel a discharged and defiant woman from the hospital. Alex learns his fate after re-taking his medical exams. At the same time Izzie is trying to stop Alex from making stupid decisions when a patient that doesn't speak English is lied to by her coach. George, Cristina, and Alex compete in a hot dog eating competition.

All the nurses at Seattle Grace Hospital go on strike, leaving the doctors to fend for themselves. George refuses to cross the picket line and finally joins the nurses on their strike while Alex, Cristina, Izzie and Meredith meets Bailey's stand-in: Dr. Cindy Aaron, the complete opposite of Miranda Bailey. Izzie agrees to work on a difficult pregnancy case with Addison, while Cristina and Alex are in the pit attending to a young married woman with a real bad case of rash. Meredith happens on an old woman that she needs to intubate and then learns she was DNR.

An explosive case arrives at the O.R. that might endanger all the lives of the people working there, which leads Dr. Burke to declare a "Code Black" for the hospital. Bailey worries where her husband is as she is in labor. Also Izzie and Alex may be creating some heat.

Derek is still operating when he finds out about Meredith's current situation. Meredith is freaking out about her situation. Webber and Bailey are dealing with medical health issues. Cristina and Izzie have their own issues to deal with because of Meredith's situation. Addison freaks out when George tries to find a solution to Bailey's impromtu postponement. Overall, Seattle Grace Hospital is still under code black and the situation is getting worse.

Derek and Addison's relationship is rocked to the core when a former friend comes to Seattle Grace and his presence promises to shake things up for a few members of the staff. Burke and Cristina's relationship is affected when one of her secrets is outted. Alex and Izzie are having similar reactions to their closet scenes during the Code Black crisis. On top of this a cocky doctor shows up to piss Derek off in all kinds of ways. A patient is suffering from constant orgasms and her condition sparks interesting conversations among the staff. George is trying to figure out how to get Meredith to see him as more than just a housemate. Another patient, that Derek is treating, is dealing with a rare disorder and needs his parents support and understanding. Burke has a patient who inspires him to talk to Meredith and Cristina about doing what they say they will. Meanwhile, Meredith learns more about her family (in fact maybe more than she may have wanted to know) through her parents.

Meredith and George are experiencing morning-after tension at home and at work and it has the rest of the doctors wondering what's up. Derek and Addison are experiencing their own version of morning-after tension as a result of Mark's visit to Seattle. Bailey, returning the favor that was done for her during the Code Black situation, must treat Addison for a specific feminine problem. Izzie and Alex are making headway in their relationship until Denny Duquette comes back. Soon Alex is not-so-oddly jealous of the attention Izzie is showing to Denny. Someone finds comfort in confiding in a patient who is going through an ordeal of his own. Burke deals with a patient and gets to observe the patient's unstable relationship with his fiancée.

The doctors are up to their necks in their usual levels of drama. Meredith is dealing with the backlash of sleeping with George, George and Burke are bonding in ways that bother and creep out Cristina, Cristina gets stuck on diaper duty, Bailey gets involved in a case even though she's still supposed to be on maternity leave, Addison and Derek have a talk, and Izzie is still flaking on Alex for Denny Duquette, the heart patient who didn't get a heart. In the patients-of-the-week department we've got a very pregnant woman, a hockey player who desires medically unnessasary amputation, and a woman with a fork in her neck who happens to be dying and has a struggling marriage.

After a series of deaths at the hospital some of the staff become very superstitious. Izzie worries about Denny and gets confronted by Alex. A patient with OCD drives Cristina crazy. Derek and Addison discuss their relationships with Meredith. Richard treats a friend from 17 years ago who reveals a secret about a dark time in his past that involves Ellis. George gets an earful about the women he's not talking to. Burke and Cristina argue about kicking George out.

Meredith and Izzie take up knitting. Derek operates on Andrew, a spelling bee champ with a serious head injury. Bailey gets in on Andrew's surgery because she's worried that her coworkers won't recognize her Nazi-status now that she's a mother. Addison's patient has an unborn baby with medical issues. After Alex fails to bite his tongue when a terminal patient routinely lies to her daughter about her health he gets a lesson in bedside manners from Burke. George also begins to overstay his welcome at Burke's apartment after Callie visits him. Meredith has more confusing and uncomfortable encounters with members of her family. One of the female doctors meets a veterinarian named Finn. Izzie flirts with Denny and they play more naughty-Scrabble. Meredith, Derek, and Addison sarcastically take another small stab at their friendships.

Addison's patient is a Catholic mother of seven. Addison gets in trouble after learning that the patient's husband won't use contraceptives. Derek treats a divorce attorney who asks if Derek is in need of her services. While Izzie and George are talking about their personal lives they "overhear" part of Derek's conversation with the divorce attorney who calls herself one of Seattle's best. Alex gets in trouble with Addison yet again for not being able to keep his mouth shut when other people think he should. A legendary jazz musician refuses to see medical reason. The musician is Burke's musical hero. Finn makes Meredith breakfast.

The staff attends to an intern from another hospital who has short-term memory loss. This intern, named Marshall, also has caused a car accident that involved a married couple, their unborn baby and the woman's parents who the staff are also treating. The pregnant woman is named Melanie and she will die but her baby may survive. One of the female interns meets up with a woman from her past who is planning on having a family of her own. Cristina is in a good mood although Alex, Izzie, George, and Meredith are having problems but in the meantime Burke hasn't forgiven Cristina for her late night faux pas. Meredith and Izzie are making fun of Callie's household habits and George and Callie are having a fight because of George's roommates. Addison is continuing to own Alex and he's upset about it. Denny has an outburst at Izzie and Derek has an outburst at Meredith.

George and Derek work together, Denny still doesn't have a heart, and Meredith gets paired with Callie. A 12-week pregnant girl dies in the O.R. and her parents try to keep the baby alive. This causes tension between Derek and Addison. One doctor's overreaction unites two bickering patients. Finn is still treating Doc for medical problems.

Denny needs a heart or else. Izzie and George go crazy trying to get him one. Derek has the life of a friend in his hands as he operates on Burke who has been shot. Burke cannot operate on Denny after Denny's heart stopped and now Denny is in a dire condition. Cristina gets put in charge of the ER and she is worried about Burke.

This episode is the second part of a two-hour season finale. Richard tries to get information from Addison about a family member's condition. Callie and George have a talk about his feelings. Meredith and Derek have a talk about Doc.

Meredith must make an important choice about which path she wants to follow to determine the future of her love life. While she considers her future she and others have flashbacks of their pasts. Cristina spends time with Burke while he recovers. Webber and Adele have a conversation after he spends the night at the hospital. Everyone attempts to deal with Izzie's choice to quit. George seeks relationship advice from Derek.

Cristina meets Burke's parents, the interns try to get Izzie's job back, and Addison takes a day off, a surgical patient may be living her last day. Some of the interns want to know why Bailey won't talk to Izzie. Meredith tries to decide between Derek and Finn and comes to a decision somewhat. Webber finds out that Callie has been living in the hospital and he confronts her about it.

The staff tries to prevent a patient from getting an elective surgery. Cristina tries to help Preston cope with the after effects of his surgery. A patient bails on their surgery. Someone goes to a bed-and breakfast. Alex deals with a patient who has had a high amount of injuries in the past. A man undergoes surgery. Before the surgery his wife was only somewhat supportive, but the results may be too much for her to handle. Izzie tries to go back to the hospital for the first time since Denny died. One child's constant visits are noted by a nurse. Two foster patients are met with suspicions of child abuse. George and Callie's relationship moves forward.

Shawn Sullivan, a car salesman who just had surgery, wants to get back to his routine so he doesn't lose his renown. Addison works with a pregnant woman named Rebecca who may need a C-section and Addison doubts her medical skills. Rebecca wants to have the baby naturally. Derek and Mark's opinions clash when the try to decide the course of treatment for a burn victim. Izzie gets surprised. Cristina pushes Burke to get better faster.

Derek learns one of Addison's secrets. Bailey talks about motherhood and depression to a mother who is set to have cancer surgery and who seems to not care about any decisions concerning the future. A resident is fiercely questioned about the death of a male patient. An ex-couple meet before lunch and get stuck - Meredith and Addison work on their case. Things get awkward when the ex-couple's daughter, Michelle, arrives at the hospital.

Cristina gets to scrub in on a rare surgery which incites envy. Alex questions his future in plastics. George and Addison work together with Noelle. Noelle is pregnant with twins but one of them is growing slower than the other. Her fiancé has problems of his own. Derek's sister visits. A patient's wife makes things hard on the staff since she has made her husband's health her job. A woman's sexual exploits are questioned.

The men of Seattle Grace go on a camping trip together, Addison and Callie must team up to work on a patient, Meredith assists Sloan with a procedure unlike any she has experienced, and, suspicious of her recent actions at the hospital, Bailey confronts Cristina. A 9-year-old is seen by Cristina after he swallowed Monopoly game pieces. A pregnant 25-year-old, is brought in after she slipped in the shower. She doesn't want medicine to take away the pain from her injury so not to put her baby's growth in jeopardy. Doctors take care of Daniel, a man who wants a sexual reassignment surgery and who now goes under the name Donna. Accompanying Daniel is his wife of the past 10 years, who was surprised to see him want that surgery but, after much struggling, decided to stay by his side.

George's father has a serious heart problem that requires surgery and George chooses Burke to do the procedure. Burke doubts himself because he knows the pressure this kind of surgery will put on him, but Cristina believes the team can handle it. Derek works with Meredith on being a couple again and tries work with Addison on more civil terms. A patient has had mutiple plastic surgeries so that his girlfriend will like him more. A mom wants her daughter's babysitter fired, after she is brought in with multiple injuries, but the girl likes the babysitter more than her mother.

A traumatic car accident fills the ER. Izzie pushes the boundaries of her probation. Cristina has a crisis of conscience about her deceptive teamwork with Burke.

Recent events strain Burke and Cristina's relationship. Mark and Derek must work together when two close-knit brothers seek medical help. One of Meredith's half sisters is admitted to the hospital.

Meredith discovers that Derek has a problem sleeping while her father comes to visit the hospital. George's father is moving from one surgery to another. A patient named Heather checks into the hospital. Heather is 17 and has a nasty attitude that results from her medical condition and all the surgeries it has required her to have. Izzie has an emotional breakdown when she tries to hand over something very important to her. George's family comes to visit to celebrate his father's surgery. Cristina and Burke are playing Uncle.

Cristina and Burke continue to play Uncle until one of them gives in. Derek and Meredith are fighting over the reason for their sleepless nights. Meredith tries to talk to her father about his side of the story. There's tension between Alex and Addison. There is even more tension between Addison and Mark. Addison confides in Callie. Bailey wishes she didn't have to keep a secret from one of the interns. Callie rushes to be with George after she learns that his dad needs an emergency procedure. Izzie may have found 'some good to do' with her inheritance.

After the Chief announces his retirement, rumors begin to circulate on his departure and successor. Mark is determined to leave Seattle for good but Meredith accidentally has him stay after letting him know of the open Chief position. Derek is angry at Meredith for causing Mark to stay in Seattle, but soon realizes that she is not the reason he is really angry. The attending physicians at Seattle Grace Hospital fight to get Richard's attention, but he expresses his disappointment. He also displays his lack of support in Bailey's plan to create a free medical clinic, but she ultimately goes through with her plan when Izzie offers to spend her entire 8.7 million dollar inheritance on the project. George, devastated after his father's death, uses sex to overcome his grief, and eventually proposes to Callie. Cristina and Burke still don't speak to each other, but he breaks the agreement when he proposes to her. Richard endeavors to reunite with his wife, Adele, and decides to retire, only to come home and find his wife with another man.

The race for the Chief's position is on, and the attending physicians, Derek, Burke, Addison and Mark, compete for Richard's affections by trying to help out everywhere possible. The Denny Duquette Memorial Clinic is open for business, but only one single patient shows up. Izzie is disappointed in what she invested Denny's legacy in, and tries to steal patients from the emergency room. Callie and George get back from Las Vegas, announcing their marriage, much to everyone's disbelief. Izzie is not supportive of their marriage and tries to get George to realize the mistake he has made. Meanwhile, Meredith's Alzheimer's-stricken mother, Ellis Grey, experiences a change in her medical condition by becoming lucid for the day. She is disappointed in the mediocrity her daughter has fallen into and begins to despise Derek, blaming him for what happened to the Meredith that used to be "a force of nature". Ellis has to have heart surgery and, despite her wishes, Meredith schedules her upcoming surgery. Richard talks to Ellis and realizes that she is still in love with him, but loses her memory after their talk ends, before Meredith has the chance to tell her how she really feels.

A mass trauma situation, which turns out to be a ferryboat accident, challenges the whole staff of Seattle Grace Hospital. Richard finds difficulty in coping with his separation from his wife and dyes his hair "for the ladies", which becomes an internal joke between Mark, Burke and Derek. Cristina tries to tell Meredith about her upcoming marriage, but doesn't have the strength to. George promises to find a woman's son, who has been separated from her at the accident. The woman refuses to go into surgery until she is assured that her son is alive. Izzie has to take care of a man who got stuck between two cars on the ferry, but nobody helps her due to the large number of injured people. Alex rescues a pregnant woman with severe wounds on her face, and promises to take care of her. Meredith looks after a girl who has been separated from her mother after the accident, but accidentally falls into the water and drowns, with nobody but the little girl as a witness.

Meredith is still underwater, but nobody seems to notice. Her worsening condition makes her rescuing an urgent matter. Derek finds her coat on a man she had helped, and starts looking for her and, much to his shock, the little girl Meredith took care of suggests that she is in the water. Derek saves her, but she is almost dead, due to hypothermia. Izzie has to perform brain surgery on a man stuck between cars, as he begins to experience seizures. She drills holes into his head, perforates his skull and ultimately saves his life before he is rescued and transferred to Seattle Grace Hospital. George lies to the woman whose son he had been looking for, in order to get to surgery, but still doesn't have any luck in locating him. Alex finds no hope in searching for the pregnant Jane Doe's family as she undergoes surgery. The interns find out about Meredith's situation and express their hopelessness. She wakes up in what appears to be limbo and meets her deceased acquaintances.

Everyone is pushing for Meredith to survive, or in this case to be revived. People are still dealing with the fallout from the ferry disaster. A young man named Lucas is having problems with brain-mouth coordination. Someone else dies.

The race between the attending physicians for the Chief of Surgery position heats up after a new competitor enters the fray. They soon realize that the new surgeon, Colin Marlow, was Cristina's professor in medical school and they used to have a long-term relationship. He begins to lie to Burke in order to protect her secret, but is soon faced with the realization that their relationship is on the rocks. George finds out that Callie's family is rich, but she had previously hidden the fact in order to find out whether George loves her for who she really is. Derek treats his former colleague from New York, and forces her to have surgery for brain cancer in order to save her future, no matter what the post-surgery risks are. Alex continues to work with Jane Doe, whose memory doesn't seem to come back. He moves in with Meredith and they have a dinner with her father and stepmother. She seems to connect with Susan, but her relationship with Thatcher seems to be irreparable. Izzie wakes up, realizing that she has slept with George while they were both drunk.

In the aftermath of Izzie's affair with George, he doesn't seem to remember anything. Callie lets him know that they will be having dinner with her father, but George does not make a good impression, being hung over after last night's events. Alex helps Jane Doe choose how her face will look like after Mark Sloan performs reconstructive surgery on her. He also gives her a new perspective on how the world will see her from then on. The hospital board begins interviewing the candidates for the Chief's position, and Colin Marlow intimidates everyone with his ten-year plan. However, after taking advice from Bailey, Mark seems to have convinced the board that he is appropriate for the job, despite continuous efforts from Derek, Burke and Addison, whose careers in the hospital outlast his. Izzie seeks advice from Addison about her affair, telling her sleeping with George felt right, despite him being married. Mark takes Meredith as his intern for the day in order to impress the Chief, something that Derek doesn't approve of, feeling that Mark has become manipulative.

Colin Marlow continues to try to get in the way of Cristina and Burke's relationship. The daughter that Izzie gave up for adoption needs something from her. This episode features a pro chess player, a flirtatious woman, and a mother named Mrs. Malone. Mr. and Mrs. Malone haven't talked to their daugther in a while because of their son-in-law. Someone goes to see a priest.

The attendings vie to be Chief. Two people who haven't slept together before, will. McSteamy's 60-day vow of chastity has a conclusion. We meet a boss, his assistant, and his wife. We also get to see someone being treated in the clinic. Derek has more questions about his relationship with Meredith. The chairman of the hospital board is admitted as patient. Callie confronts Izzie about her relationship with George.

Meredith works on her relationship with Susan and Thatcher. Cristina has to deal with her mother and Burke's. Alex continues to tend to Jane Doe/Ava. Meredith and Derek's relationship has a problem that needs resolution quick. Addison sees her god-daughter which leads to a job offer outside of Seattle. Derek has to perform surgery. Burke has a reservation about marrying Cristina. Many new people guest star in the course of Addison's road trip to California. Addison considers moving to be closer to her old med school friends until she discovers that drama she wishes to leave behind isn't exclusive to Seattle. Her friends who she thought had it all, are divorced. A pregnant woman must discover who the father of her child is.

Meredith works on her relationship with Susan and Thatcher. Cristina has to deal with her mother and Burke's. Alex continues to tend to Jane Doe/Ava. Meredith and Derek's relationship has a problem that needs resolution quick. Addison sees her god-daughter which leads to a job offer outside of Seattle. Derek has to perform surgery. Burke has a reservation about marrying Cristina. Many new people guest star in the course of Addison's road trip to California. Addison considers moving to be closer to her old med school friends until she discovers that drama she wishes to leave behind isn't exclusive to Seattle. Her friends who she thought had it all, are divorced. A pregnant woman must discover who the father of her child is.

The interns finally take their first year medical exams, the biggest test of their careers, and one of them is ill-prepared. Callie grows more suspicious of George and Izzie. The doctors treat a patient named Dale. Three mountain climbers are treated. Cristina works on her vows. Adele wants Addison to keep a secret from Richard.

The mountain climbers lie about the axe in their friend's head, telling Derek that it accidentally got there. During surgery, he and George discover that it was deliberately put there, and one of the climbers admit that he was trying to "put him out of his misery". Adele is saved after Richard finds her lying in the bathroom and is stabilized, but soon suffers a miscarriage. Richard learns Adele was actually pregnant with his son, not someone she had one night stand with. Bailey is disappointed to see that Callie is the new Chief Resident and begins to question her abilities as a surgeon. Richard chooses Derek as Chief of Surgery, but he refuses, telling him that he isn't done doing what he does best. Cristina and Burke's wedding day arrives, but Cristina won't stay out of the hospital. However, Cristina's nervousness results in Burke's realizing that he does not love the real Cristina and leaves her. Meredith and Derek are uncertain about their future and despite Derek admitting that she is the love of his life, they call their relationship over.

Addison visits Seattle Grace because they need skills that only she has. Rebecca/Ava returns with news for Alex. Meredith and Derek's clinical trial experiences one or two developments.

Addison, Naomi and Sam rush the ailing Archer to Seattle Grace and reunite with old friends Derek and Mark to help save his life; meanwhile, Izzie employs her fellow doctors in a medical game designed to help teach the interns, and Owen runs into a significant someone from his past

Derek's confidence is shaken like never before as he faces off with Addison over what course is best for their dying pregnant patient; Cristina calls the abilities of a renown surgeon into question after she botches a standard procedure; and Bailey, who has decided to pursue a fellowship in Pediatrics, is appalled by the Chief's less-than-stellar recommendation letter.

Mark flies Addison to Seattle to help with a difficult procedure on his pregnant daughter, Sloan, Owen questions Teddy's motives when she assigns Cristina the lead on a complicated surgery, and Derek's suspicions are raised when the Chief recruits Meredith to assist with a high profile operation on.

A cataclysmic event leaves the doctors shaken; Callie, on the verge of a life-changing moment, starts imagining about the hospital and her friends.

As Meredith puts Zola to bed and falls asleep, she begins to wonder -- what if her mother had never had Alzheimer's and she'd had loving, supportive parents? The reverberations of a happy Meredith Grey change the world of Seattle Grace as we know it. What if she had never met Derek in that bar and he had never separated from Addison? What if Callie and Owen had become a couple long before she met Arizona? And what if Bailey never evolved from the meek intern she once was?

Seattle’s favorite redhead returns and graces the Grey Sloan halls with her experience and expertise as she attempts to help Richard teach the newest crop of residents. Meanwhile, Meredith has a decision to make, and Link confides in Teddy.

Richard recruits Meredith and Bailey to help him launch a new program. Meanwhile, Addison’s patient has complications from a procedure, and Jo helps a woman who goes into premature labor.

Bailey faces an unhappy Catherine who is facing audits for several of her Foundation hospitals. Meanwhile, Addison is back at Grey Sloan; tensions rise between Meredith and Richard, and Owen returns to work.

Bailey recruits the interns to create a series of social media videos informing teens about sexual health. The videos, filmed at Grey Sloan in front of a group of high schoolers, hit home as a student has medical complications during her visit. Elsewhere, Meredith and Maggie learn something new about Zola.

Bailey and Addison take a road trip to volunteer at a family planning center, but a patient’s ectopic pregnancy leads to complications. Elsewhere, the interns play detective about Lucas’ relationship with Amelia, and Meredith catches up with Jackson on a trip to Boston.

Addison makes a special appearance at Grey Sloan to welcome Bailey’s new OB/GYN trainees. Maggie’s lung transplant is derailed, and Nick bonds with Lucas — before the day takes a shocking turn.

In the immediate aftermath of shocking events at the clinic, the hospital goes on lockdown and the Grey Sloan doctors split up to save multiple lives; Maggie lands in hot water with Winston; Jules' roommate makes a surprise appearance.

Amelia takes her personal problems out on her work colleagues, and the threats against Bailey come to a terrifying head. Lucas and Jules make a risky decision on a patient, and Mika struggles with burnout.