Bosco is caught on a security camera having sex in his squad car with the daughter of his Precinct Captain. Meanwhile Doc drags Carlos around the city on a personal mission to find the owner of a watch, found in the ambulance.

The two rookies, Carlos and Davis, experience disillusionment with their new jobs, and their training officers. Bosco struggles with Homophobia and gets himself involved in tit for tat games with Doherty.

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.

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.

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.

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.

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 mob boss, 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.

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

On September 10, 2001, Ty and Sully are in Atlantic City on the eve of Sully's wedding to Tatiana. Kim sinks deeper into depression. Bosco searches for anything to do after someone lets out the result of the Giants game he had taped to watch after shift. Jimmy keeps trying to catch up on some sleep after nursing a sick Joey.

Faith negotiates the end of a live on TV hostage situation. The leader of a vampire cult holds Emily hostage until Bosco saves the day. Cruz attempts to negotiate a deal with a gangbanger to end the war on the 55th Precinct, but instead, he organizes his troops to attack.

Sully and Maggie reconnect; Bobby visits his brother Matty and tries to prepare him for his release from prison; Sunny asks Kim for a place to stay and runs away when Kim refers her to a shelter; Carlos hits a pedestrian with the bus; Faith and Bosco investigate a grave robbery and ponder immortality; Jimmy rescues a new recruit who is trapped under a collapsed ceiling in an apartment fire; Bobby takes Doc's advice and tells Kim how he feels, only to learn that Kim feels she isn't good enough for him; Sunny ODs and Bobby helps a saddened Kim find out her real name and hometown so that her parents can be notified; Sully's approach to ""problem solving"" goes horribly awry in a domestic dispute; Carlos and Doc come to blows over Doc's training methods, forcing Morales to break them up; Sully learns that Ty has good instincts, enabling them to save a teenage girl from a sexual predator.

Ty is worried about Sully's dating Maggie; Faith and Bosco lose a witness who turns out to be the perp in a homicide; Bobby prepares for Matty's release from prison; while driving the bus, Carlos collides with a pregnant driver and later attempts to revive the baby she delivered prematurely after Sarah pronounces it dead, unaware of the consequences for the parents; Jimmy rescues a boy from a tree; Bosco and Ty take issue with Sully over his handling of a belligerent collar.

On Thanksgiving Day, Bosco tries to resolve a family conflict in a restaurant while Faith deals with the same thing in her own home. Bobby's mother refuses to allow Matty to attend the family's holiday celebrations, and leaves it up to Bobby to tell his brother. After a shooting, Ty and Sully disagree over how they should report the incident to their superiors and the investigating team.

When he goes on his first raid, Davis inadvertently endangers a young boy he is trying to help; Doc begins to think that the overdose his father took may not have been accidental; to get a critically ill woman to the hospital, the firefighters knock down an apartment wall and lower her out a high story window.

An explosion in a building about to be demolished leaves men trapped inside, forcing the firefighters to make terrible choices; Fred's drinking problem escalates; Doc cancels his date with Brenda.

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.

Faith, Bosco, Sully, Ty and Candyman race through the neighborhood on foot in pursuit of a trio of Uzi-armed thieves; Candyman risks his life to save Ty; Bosco's cold refusal to get medical assistance for one of the perps leads to the robber's death; Ty searches for the truth about his father; Bobby's mother tells the police where to find Matty, who desperately pleads with Bobby to give him some getaway money; Bobby agrees, but begs Matty to turn himself in; Matty gets high and takes off, leaving Bobby crushed and seeking consolation from Kim; and Carlos finds out about Doc and Morales.

It's Valentine's Day and Bobby and Kim have spent the night together; Bobby's confession of love leads Kim to realize that they've made a big mistake; after agonizing all day, she finally confesses and breaks Bobby's heart; seeking solace in a bottle, Bobby finds himself at a local bar next to a woman who has also been jilted that day, and they go off to her place; Fred drunkenly totals the car on the way to pick up Emily and Charlie; Faith arrests him and refuses to bail him out; when he finally arrives home, Faith has his things already packed and throws him out; Carlos tends to a girl who runs into a bus and then falls for him; the gay community is targeted by a gunman and a vigilante group forms to find the killer; Ty arrests a girl for auto theft who turns out to be Malcolm's sister; and Faith lets Bosco know that she is fed up with his bigotry.

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.

Dealing with the aftermath of gang warfare, Doc and Carlos disagree over reaching out to prevent an eleven year old boy from following his brother into a gang; Bosco's decision to turn the tables on two men who try to rob him when he's off-duty could cost him his badge when the two men turn up at the precinct to report the crime; as he continues his losing streak, Jimmy gets deeper and deeper into his bookie, which puts Joey in danger; Kim begins to worry about how much time she spends with Joey after he gets into trouble at school.

The three squads are stationed at the Waldorf-Astoria Hotel to provide protection during a Clinton-Giuliani Senate race debate. The cops are assigned to the kitchen and discuss politics and the death penalty while Sully tries to get a reluctant head chef to feed them. The paramedics are parked in the hotel's garage where they talk about their worst cases, religion, relationships, and how life doesn't turn out as planned. Kim and Jimmy have it out again over his irresponsibility after her paycheck is garnished to cover one of his bad debts, and Jimmy resolves to clean up his act.

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

Feeling betrayed, Doc angrily confronts his former friend, Jerry Mankowitz, an attorney's investigator who tricked him into confiding vital information about a pending malpractice suit.

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.