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.

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.

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.

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.

Carlos falls behind in his studies and then hears some shocking news from Vangie; the cops search for a two-year old girl missing after her family is involved in a car crash; Bosco and Faith contend with a disabled man dealing drugs to children; Sully and Davis track down the alcoholic who attacked the pastor of Sully's church.

Doc and Carlos are rescued by the firefighters when they get trapped in an eighteenth floor apartment with a patient who cannot walk; Ty comes to the end of his probationary period; Faith discovers that she's pregnant again; the firefighters come under fire from a madman when they arrive to fight a car fire.

Sully lives his worst nightmare as the police search the city for a man who is buried alive and whose kidnappers are involved in a fatal car crash; Kim and Bobby find an abandoned 4 year old boy wandering the streets; Sully's mother wanders off from her nursing home; Carlos adopts a deceased patient's cockatoo.

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

Bobby comes to the aid of his old friend Paulie after Paulie's sister begs Bobby to help her brother with his drug addiction, but becomes enraged when Paulie breaks into Bobby's mother's house and robs her to support his habit.

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.

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.

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.