Two new recruits join the emergency services and work with older, wiser partners. Davis becomes a policeman, like his father, and Carlos a paramedic. Two other Paramedics, Bobby and Kim, find themselves rushing from emergency to emergency. Bosco and Yokas, the other police officers, and Jimmy and his fellow Fireman have their own crisis' to deal with.

Doc, Carlos, and Ty each feel guilty about the mistakes they made during Jerry's shooting; Jimmy gives Kim a bulletproof vest; the squads rescue a man dangling from the side of a skyscraper after an explosion; Fred wants Faith to quit her job; initially reluctant to discuss the circumstances surrounding Ty's father's death when Ty asks, Sully finally relents; Carlos and Ty commiserate about their partners; Sully's contacts on the street pinpoint an abandoned building as the location of Jerry's shooter, and Bosco takes the shooter down -- out a second floor window.

Mercy's new E.R. attending gives the cops and paramedics a hard time while ignoring Carlos's attempts to hit on her; Doc is saddened to hear that Jerry has decided to take a disability retirement; Jimmy is upset when Joey goes to Bobby first after he becomes ill as a result of Jimmy's letting him overindulge in sweets; Jimmy and Bobby take out their conflict over Kim and Joey in a game of one-on-one; Sully and Ty arrest a purse snatcher who will do anything to stay in jail once he discovers that his victim's son is a mobster; Faith hands out street justice to a gangbanger responsible for the deaths of two little boys.

Jimmy's failure to watch the firehouse door leads to tragedy; Morales, devastated by the loss of a young patient, reaches out to Doc for consolation; Sully's first partner commits suicide, prompting him to seek out Maggie and reflect on where his life has gone; Bosco tries to buy a '67 GTO from a homeless man; and Bobby continues to do whatever he can to get his mother to reconcile with his brother.

As he comes around a corner in pursuit of a gunman, Davis shoots a man who is pointing a gun at Sully, unaware that the man is innocently returning the service revolver which Sully dropped when he fell. Davis's guilt leads him to doubt whether he should remain on the force, until Sully straightens him out. The tension between Bosco and Faith continues to escalate. Both Bobby and Jimmy introduce their new girlfriends to Kim, who isn't thrilled with the potential competition.

Yokas and Bosco chase a carjacker into a multi-level garage. When the thief drives off the edge of the top level and crashes to the ground, Bobby risks his own life to save the driver. Much to the surprise of everyone who knows him, Bosco goes to the opera with Nicole and her parents. Carlos gets into trouble with his boss and Vangie. Sully and Ty go to help Candyman on a job, and Ty tells Candyman exactly what he thinks of him. Jimmy has news for Kim which surprises her, and annoys Bobby everytime Kim tries to talk to him about it.

The deaths of four teenagers in a fiery car crash profoundly affects the third watch, who were forced to stand by helplessly, unable to save the victims. They congregate at the end of the shift to dispell their sadness and anger at the horrific images of the crash. Faith, Sully and Doc spend time sitting quietly in a cafe; Ty, Bobby, Carlos and Alex go to a bar; and Kim, Bosco and Jimmy go bowling. As evening turns into day, Faith's group meets up with a young woman, Ty's group meets up with a young man, and Kim's group meets up with a young couple in love. At dawn, everyone ends up at the a beach and they build a bonfire. As the flames flicker, we see a flashback to the moments immediately preceding the car crash and discover that the young people whom they met during the course of the evening are the spirits of the teenagers who died in the crash, who were sent back down to earth to tell them that the crash could not have been prevented, and they are not to blame for being unable to

Bosco, Yokas, Sully and Davis search for a cop killer on the streets, and cope with an obnoxious new sergeant at the station house.

Sully is upset when he is wrongly accused of falsifying evidence; Bobby helps one of his former teachers dying from cancer; Carlos deludes himself into thinking that Kim is falling in love with him; Sully gets closer to his pretty neighbor.

Bobby's attempt to keep Paulie away from drugs ends tragically.

Faith's excitement over having her husband to herself for the weekend is dashed when Fred decides to spend the time trying to win a truck; angry, Faith organizes a drunken girls night out, meets a handsome photographer, and ponders an affair and what might have been; Fred outwits his opponents and wins the truck.

It's September 21, 2001 and the squads continue to battle through their emotions and their misgivings about their hero status, while working double shifts and spending every free moment at ""the pile"" searching for the missing; Kim returns to work and teams up with Doc, which allows an emotionally frayed Alex to return to paramedic duty; an exhausted Sully attempts to co-exist with his prospective in-laws while he waits for an opportunity to marry Tatiana.

After a despondent woman takes a walk off of an eight-story apartment building, the squad finds themselves in a race to transport both the woman's heart and a dying girl to a local hospital in time to save the youngster's life. The suicide hits home for Faith as she comes to grips with her own ongoing medical problems, while Doc expresses concern over the emotional effects this case will have on Kim, despite her constant reassurance that her accident was not an attempt to kill herself.

Bosco runs from the present and his past when he is wrongly suspected of murdering a sexual-assault suspect. As Faith tries to gather evidence to clear him, Bosco turns to his dysfunctional family, including his alcoholic mother, drug-addicted brother and estranged, abusive father. An emotionally rattled Kim virtually kidnaps Joey from Jimmy while Carlos actively solicits Ty to be his new roommate.

Doc visits Ryan, who's now walking during his physical therapy sessions.

Carlos decides to take a ride on the fire pole and falls, losing consciousness. Doc, Kim and Alex bring him to the ER where he is finally awake and combative. Dr. Thomas admits him to the hospital for observation because of his head lac and LOC. The nursing staff settles a score with Carlos by putting him in a room with Rodger, a drunk he brought in the day before. Rodger is alternating between screaming, crying, whimpering and non-stop talking -- all at the top of his lungs. He's going through the DTs and can't be sedated, because he admits to being drunk since 1987.

Feeling betrayed, Doc angrily confronts Jerry Mankowitz for tricking him into confiding vital information about a pending malpractice suit by not revealing that his old partner is now working as an attorney's investigator. Later, when Doc heroically responds to an emergency involving a near-comatose elderly woman trapped in ice, he remembers that his job is worth the legal fight ahead. Meanwhile, Carlos worries that he got the wrong telephone number from his latest romantic conquest. Faith thinks that troubled Bosco has lost his enthusiasm for police work. Jimmy struggles to act as both mother and father to Joey.

The police officers sort through the carnage and count their dead in the wake of a shootout between rival gangs. While Faith tries to interrogate Fyodor Chevchenko, a ruthless Russian mobster, Sully worries about the severely wounded Ty and regrets causing the incident. Tatiana chastises Sully for hassling her injured son. Faith worries about Gusler, her ineffective, frightened rookie partner, and a weary Doc gets some unexpected good news about his medical malpractice suit.

Hopelessly in love with Kylie and concerned that she will lose her Latina heritage if she is adopted by a white couple, Carlos considers raising her until he realizes that the couple can give her the sister, the grandparents, and the extended family that he cannot; Kim's preoccupation with her new PDA drives Alex crazy until they are able to use it to save a very sick man, thus redeeming themselves in the eyes of a hypercritical Dr. Peterson; Faith and Fred are still on uneven ground about the sergeant's exam; in an effort to shake Chevchenko's tree, Faith and Sully execute a clever plan to disrupt the Russian's bookmaking operation, which also opens the door to the possibility of the still-missing Tatiana's return; Bosco is cleared for duty, and he and Faith agree to be partners again as soon as he returns.

Rescuers find the body of Alex's father, and he is given a hero's burial; Faith and Bosco tail a convicted rapist released on appeal, certain that he will rape again; dissatisfied by Tatiana's explanation of her whereabouts the eight weeks she was missing, Sully investigates further and uncovers some astonishing and heartbreaking facts about his wife; after Chevchenko threatens to kill him if he doesn't roll over on Faith and Sully, Frankie tells Swersky that the raid on Chevchenko's numbers business was a hummer bust, leading Chevchenko to threaten a lawsuit and have another angry confrontation with Sully.

Bosco roams the city looking for Faith, and finally tracks her down just as Faith manages to carry Fred out of the building after rescuing him from the elevator. After they race him to to Mercy, an overwrought Faith lashes out viciously and unfairly, first at Proctor and then at Bosco. As painful as her words are to hear, Bosco realizes the truth be

Chevchenko has Tatiana's son killed; Fred comes home from the hospital; and Davis gets a job offer.

Emily discovers just what Faith's job entails and how much her mother loves her when they are taken hostage during a bank robbery, and Faith risks her life to save her daughter.

As Faith waits for Emily to awaken from her coma, she blames everyone but her daughter for the overdose and reflects on the substance abuse problems in her family; after Cruz's sister is brought into the hospital with an overdose, Cruz gets Sully, Ty and Bosco to look the other way on any possession charges and sets off with Bosco to find the location of her supplier's meth lab, where they end up in an inferno when the dealer sets the house on fire; Kim is reluctant to give a statement in Carlos's case because she's feeling pressured to lie to save his career.

In a last-ditch effort to save Sully's life, job, and pension by getting him dried out, Ty and Bosco kidnap him and bring him to a cabin deep in the woods where he hallucinates about the circumstances surrounding the deaths of Tatiana, Chevchenko and Ty's father, and his subsequent descent into alcoholism.

Maritza's reckless pursuit of Buford triggers a horrific car accident that leads to multiple injuries to motorists, and triggers an explosion that severely injures Lt. Johnson and kills Alex Taylor; Doc and Kim get to the top of the promotion list; Maritza hangs Bosco and Nunez out to dry over the murder Noble committed; Doc's overwhelming guilt and grief over Alex's death leads him to a career decision; Maritza discovers that Faith has agreed to help Bosco clear Nunez by getting Noble's gun, and goes to Noble's place to intercept her, followed by Bosco and Noble; when Bosco insists on arresting Noble and Faith refuses to turn over the gun, Maritza draws on Faith, Bosco and Faith draw on Maritza, and three shots ring out.

Although Dade encourages him to keep quiet, Bosco tells Swersky everything that transpired with Maritza, Noble, the death of Willie G, and the shootout in Noble's hotel room, and confesses that he killed Noble after Noble pulled out a gun, Faith was shot by Maritza, and that he grazed Maritza's head with a bullet to keep her from killing Faith; wracked with grief that his wife has a bullet next to her spine, Fred attacks Bosco and threatens to kill him when he discovers that Faith became injured while she was helping her partner out of yet another jam; a critically injured Lt. Johnson, in excruciating pain and with only hours to live, begs Jimmy and Doc to ease his suffering; overwhelmed at the sight of Lt. Johnson's wife lashing out in heartbreak and anger, and her husband's horrific suffering and imminent death, Doc sadly helps out his boss one last time; Swersky has Maritza arrested when she refuses to tell him what happened during the shootout; Bosco learns that Noble was working f

Bosco arrests a pedophile posing as a toy store Santa, and the grateful store owner returns the favor by helping Bosco and Sasha come to the aid of a man whose house is robbed of all his children's Christmas presents; after Sully and Ty save a young homeless girl from a fire, she rekindles Sully's Christmas spirit; Carlos receives the ultimate Christmas present when his brother arrives at the firehouse bearing the gift of being a perfect bone marrow match for Kylie, as well as the news of Carlos's real name and family history; Kim and Jimmy spend a romantic Christmas Eve together; Sasha's search for the perfect gift for her nephew gives Swersky the opportunity to play Santa.

Bosco and Monroe investigate a suspicious man who they find bleeding in an alleyway as they respond to an anonymous caller's claim that someone is shouting for help in the area. They become more and more skeptical when his story continues to change and they find a blood trail. When it is determined that the amount of blood would have been more than enough blood loss to kill a person, Bosco suspects that the man murdered someone and was bleeding because the victim tried to fight back.

Maritza goes all out on the hunt for Michael after Dade dies, as does Bosco, who's intent on finding his brother before Maritza does; Faith calls Maritza a liar in front of Swersky when Maritza claims that she saw Michael shoot Dade; Fred is still angry about Faith repartnering with Bosco, and refuses to discuss it; Breene revisits the house and urges the paramedics to talk to professionals or to each other to help deal with the stress of the shootout; looking to collect the reward for information leading to Dade's killer, Anthony tells Maritza where Michael can be found after she lies to him about her relationship with Bosco; Bosco finds Michael moments before Maritza, and his brother claims that he's innocent and that a drug dealer named Spider was Dade's murderer; Spider comes out with machine guns blazing when Maritza, Sully, Ty, Faith and Bosco attempt to arrest him, and a ferocious gun battle ensues; Maritza agrees to work with Michael as an informant after Bosco pleads for his

Faith begs Fred to return home, but he refuses for a reason that infuriates his wife; Bosco turns a cold shoulder to Maritza's attempts to offer her condolences; Carlos is spectacularly unsuccessful in his attempts to hit on Grace; on the day of his son's funeral, Donald Mann exacts his revenge with the help of a dirty cop by planting bombs designed to kill the police officers he holds responsible for the death of his son; after Mann's lieutenants force a man to crash a car carrying a live bomb into the funeral home where Mikey's wake is being held, Grace takes charge and goes out of protocol to save Rose's life, and Dr. Fields later swears to have her job for it; Kim's decision not to enter the funeral home while the bomb is still live stems not from cowardice, but from maternal instincts; when Mann discovers that some of his intended targets survived the bombings, he sends machine-gun wielding minions into the hospital to finish off the job.

After a fierce gun battle and some hand-to-hand combat, Mann's gunmen are finally subdued by the members of the 55 in the E.R., but not before Orland is murdered and Bosco is critically injured; after Kim heroically puts herself in the line of fire to save Holly and a little girl, she realizes that her days as a paramedic are over, and that her future lies in being a wife to Jimmy and a mother to their children; Grace and Dr. Fields patch up their differences and come to an understanding about her out-of-protocol field procedures; Maritza uncovers the traitor in their midst, who leads her to Mann; Faith steps over the line to avenge her partner.

When it becomes apparent that the body in the dumpster is connected to a series of homicides that Miller investigated on his previous tour, he teams up with Faith, vowing to catch the serial killer and expose the commanding officer who transferred him to prevent him from working on the case; Brendan and Grace hook up; Carlos's plan to visit Holly and tell her that they're not dating doesn't exactly go the way he planned, not that he's complaining; after junkies trying to get the morphine on the bus hold them up at gunpoint, Carlos sustains a head injury trying to protect Grace before Ty and Brendan come upon the scene and Brendan guns down the thief holding a gun to Grace's head; Faith discovers that Miller's situation at home parallels her own; the serial killer stalks and captures his next victim, then arrives at the station house to confess his prior crimes and tell Miller that his latest victim only has twelve hours left to live.

Miller goes on the hunt for Tara Connelly, and Faith tries a series of approaches to get Barton to reveal the girl's whereabouts, until Miller returns to finish off the con that gets Barton to give it up; although they're both still shaken up by the shooting, neither Brendan nor Grace is willing to discuss it or get some counseling; Finney makes sure that his son's shoot comes up clean in the IAB investigation; at Sasha's house, a picture of the knife that Maritza planted on Mann accidentally falls into Ty's hands, but he doesn't realize the implication of his find; over his protests, Carlos gets admitted into Mercy for overnight observation of his head injury, with Holly vowing to stay by his side; a guilty Faith looks on as Finney arrests Maritza for Mann's murder

After a suspect in a jewelry store robbery starts displaying symptoms of a disease similar to SARS, the NIH is called in to figure out what is causing this, and hopefully stop this epidemic. Meanwhile, Cruz faces off with a gangbanger, who may have hired a 13 year old boy to carry out a murder.

The crossover continues on Medical Investigation S01E17 Half Life (II)

The series concludes with the gangbangers taking out their assault on the 55th Precinct. After some grenade explosions, the precinct is destroyed. Cruz knows that Marcel Hollis is behind the attack, and she takes his life, as well as her own. Carlos proposes to Holly, and they are married. Everyone receives their reassignments, and Sully retires. In the last few moments, Sully narrates a look into the future.