Annie is livid when her father brings along his girlfriend on a weeklong visit; Mary and Matt pursue new romantic interests; Lucy wants to find out if blondes really have more fun.

Mary undergoes knee surgery, while Matt learns that Michael Towner was the hit-and-run driver; Wilson reveals the truth about Billy to Eric.

Eric and Annie decide to renew their vows; a widow seeks Eric's help to confront the juvenile who murdered her husband; Mary is reluctant to put down her crutches.

Mary tries to make Wilson say that he ""loves"" her, but Wilson thinks it's a big commitment and that they haven't known each other long enough to say those words to each other. Meanwhile, Simon and Ruthie are reading Matt's love letters to Heather and get caught. Matt tricks them by addressing one of the letters to ""Mrs. Matt Camden."" By this, Eric accidently finds the letter leading to think Matt and Heather got married over the summer, which worries himself, Annie and Heather's mom, Mrs. Cain. Lastly, Eric helps Lucy's friend, Laurie get closer to her mother.

Eric accuses Matt of doing drugs after finding marijuana in the house and after Matt's friend Mitch askes him to hold his marijuana. Meanwhile, at the same time Eric finds the marijuana in the house, it leads Annie to a confession of own her about her experimentation. Also, Simon teaches Ruthie about the fine art of doing laundry, eventhough Ruthie is little too young. Lastly, Lucy introduces her new clothing of all black and her new boyfriend Rod to the family.

The Camden kids get a lesson in love as Mary decides to call it a quits with Wilson. Simon is obsessed with getting his first girlfriend, while Ruthie learns the do's and don'ts of kissing on the school playground. Matt receives devastating news from his girlfriend Heather, which leads him on a long journey to Philadelphia. Meanwhile, Lucy laments over being single until she accidently gets close to the school hunk.

Lucy gets an invitation to have pizza with two rebellious friends, then blames herself for the tragic car accident that claims her friend's life, and her sister in the hospital. After Lucy's friend is killed, the family rallies around her, noticing her unusually distant behavior. In addition, Mary does a favor for her ex-boyfriend Wilson and baby-sits his son Billy so he can go to his prom. Also, Simon gets his own room while Matt moves into the attic.

Matt tries to find the right time to tell his parents that he's accepted an internship in Washington. Meanwhile, his concern for his sisters leads to a confrontation with Mary and Wilson.

Eric and Annie's parents arrive right in the middle of the crisis involving Mary and Matt; and Happy's original owner comes to take him back.

Samuel and David are home and won't stop crying. Matt gets a new job at the Dairy Shack as a delivery guy. Mary sneaks to the pool hall to meet Wilson while Lucy covers for her at home. Lucy ends up doing all the cleaning by herself. Mary hangs out with Jordan as Wilson arrives. Wilson is thinking of moving back to Glen Oak, but Mary realizes she doesn't have feelings for him anymore. Ruthie wants to run away from home because she doesn't get much attention as she used to. Annie gives Ruthie her baby book. Simon orders food from the Dairy Shack to check out Matt's new job. Matt is fired from his job and meets an old girlfriend, Shana.

The striking resemblance of Robbie's new friend, Marie, to Mary raises eyebrows among discerning Camdens. Annie's invitation for her to stay for dinner makes things weirder for them. Back in Buffalo, unbeknownst to Robbie, Mary accidently bumps into her old boyfriend Wilson (guest-star Andrew Keegan) and his son Billy at the train station and makes plans to meet him for the evening. Mary is unsure on whether she should tell Robbie, but confides in her family about this. They all say that she should tell Robbie about this, but decides to ignore their advice. Also, Matt meets Robbie's ex-girlfriend, Cheryl, at the restaurant where she works. He starts to have feelings for Cheryl and tries his best to try to get her to go on a date with him. His efforts work by the end, but is having a hard time telling Robbie about his interest in his ex-girlfriend.

Mary returns home back to Glenoak for the summer to spend some time with her family, but fears about being together again with Robbie. Eric and Annie are recipients of what may or may not be advances from unmarried acquaintances. Simon and Deena see that they still have feelings for each other, even though she has a boyfriend. Matt agonizes over telling his family about his new relationship with Cheryl, but soon decides to tell them all. Lastly, Lucy surprises herself and others when making a proposal to Jeremy and the possibility of going to college in New York with Jeremy. Although plans change when Mary, feeling rejected by Robbie, makes a shocking declaration.

Mary tries to right a wrong by explaining to Lucy that she never had adult relations with her sister's fiance. The only problem left is trying to convince Lucy. Wilson unexpectedly drops by the Camden home from New York to see if he and Mary are really over by finding out her answer. James talks to Eric about him attempting to have an affair with Annie as Serena comes clean with Annie about her trying to have an affair with Eric. Robbie and Wilson set aside their differences so that they can talk about Mary. Matt learns a few things when it comes to Cheryl's honesty when she doesn't tell her friends that she's dating him.

Eric's stress level rises when he learns that Matt has lost his job at the hospital and is relying on his friends to find him new work. Simon is adding to Eric's tensions by pressuring him to let him get his learner's permit. At the same time, Lucy breaks off her engagement to Jeremy and just cries in her room and refuses to discuss what happened. Robbie, still longing for Mary, is moping around the house as she returns to New York to be with Wilson. Annie's behavior has Eric wondering what's going on with her and suspects she's pregnant.

Simon decides to stand up for bullied student at school only to have the boy tell him that he is going to shoot his tormentors. Robbie decides to give Ruthie a playful new nickname, but at the same time Ruthie comes up with a less-pleasant one for Lucy after breaking off her engagement to Jeremy in New York. Eric gets a visit from an old friend Merle with some family issues of her own. Mary gets serious with pursuing the career as a firefighter, but things don't turn out the way she had planned.

Simon considers dating a sixteen-year-old pregnant Sally who he meets on the bus. Annie decides to accept Robbie's offer in renting the room over the Camden's garage that both Lucy and Matt were hoping to get. A carpenter pretends to fake an injury while working on the Camden's garage and tries to sue them. Mary gets more serious with being a firefighter, mother and wife to Wilson and Billy.

Eric tries to arrange a romantic evening with Annie, but Annie keeps turning down every attempt he throws at her. At the same time, Annie takes Eric by surprise with the news that she would like to quit college and to start teaching to help get her out of her depression. Meanwhile, Simon is at risk of being fired from his new job at the pizza parlor by his excessive tardiness and discovering that waiting tables takes more people skills than he's equipped to handle. Also, Robbie sets Lucy on a date with one of his friends while Matt is concerned about a woman who keeps showing up at the clinic a lot. Lastly, Mary performs terribly in fire fighting training distracted by her consuming relationship with Wilson.

As Annie begins teaching, she inadvertently gives a student some bad advice. At the same time, Eric and Annie painfully discover how much their constant arguing is affecting the family. Lucy and Robbie finally face up to their feelings after she intentionally sabotages one of his dates out of jealousy. Cheryl goes to Eric for some guidance in her relationship with Matt, but she misinterprets the reverend's input in the matter. Simon is attracted to a girl who is dating one of his friends. Mary is left to mull over Wilson's marriage proposal and it's even more confusing when she has a romantic encounter with a fellow firefighter trainee who shows an interest in her.

Lucy and Robbie argue over who should tell Mary about their emerging relationship. Meanwhile, Matt worries that a young woman in his study group might be a victim of physical abuse at the hands of her belligerent boyfriend. Eric's sister Julie shows up at the Camden house with her toddler Erica and annoys Annie as she tries to prepare a lesson for her class. Simon meets up with Sasha and they both try to catch up on their personal lives.

Mary's sudden arrival has everyone in the family wondering what happened between her and Wilson. Only Mary knows and she's not telling. Her presence delights Annie, who goes out of her way to make her daughter comfortable, even offering her the converted garage apartment. But not everyone is happy to see her. Ruthie feels that Mary owes everyone an apology for the actions that led to her moving away.

Annie quits her job at the private school without discussing it with Eric first and he feels completely left out. Mary tries to call Wilson and learns from his landlord that he has moved out of his apartment. Simon uses Robbie's car to practice driving and gets him in trouble when Simon smashes into Matt's car. Robbie's brother Ronald stops by at the Camden home for a visit. Mary gets an unexpected visit from Ben, the fireman she kissed. Ruthie's old teacher Ms. Riddle starts working at Ruthie's school.

St. Valentine's Day delivers a few surprises for the Camden family. A grounded Simon is asked out by a senior. Annie's attempt to surprise Eric with romantic Valentine's plans backfires and results in a big fight. Mary discovers Robbie's plans with Joy. Lucy and Mary learn that Jeremy and Wilson both have dates for Valentine's. Matt seeks his fathers help as he wants to settle down, which leads him to seek out old girlfriends as to why they're no longer together. Ruthie is hesitant to go to a party because her friend tricked her into asking out a boy she's already going out with.

Eric seeks help from Mary's (Jessica Biel, who does not appear in the episode) ex-boyfriend, Wilson (guest-star Andrew Keegan) after Charlie (guest-star Eric Panler), a new father, confesses to Eric that he has made a mistake and can't handle the responsibility of being a young dad. Meanwhile, Lucy and Kevin argue over which doctor they prefer, and Ben (guest-star Geoff Stults), who has taken an unusual interest in their pregnancy, only makes matters worse by siding with Lucy; and Ruthie has hidden intentions for wanting to hang out with Martin and his best friend Mac (guest-star Kyle Searles), which only leads to disappointment since Mac thinks of her more as a little sister.