Kim and Jimmy are having a custody battle over Joey. Boscoe and Faith are on a call of a possible terrorist threat, that ends up being an explosive event. Alex risks herself to save a little girl and is punished by Doc for it.

Doc is up for paramedic of the year and is being followed by a film crew. Doc may have made a medical mistake when treating a patient. Faith recovering from cancer treatment and on the job fails to back up Boscoe while chasing a suspect.

Bosco tries to protect an old ESU sharp shooter from spiraling out of control. Faith contemplates taking the sergeant's exam. Davis and Taylor have a steamy affair. Doc feels the guilt over a mistake that made a boy a paraplegic.

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.

During the investigation of the gang shootout, the police officers are questioned and presented with evidence that suggests that Ross was killed by friendly fire; Carlos learns that Vangie is dead and that he is the father of the baby her sister leaves at the firehouse; on the first anniversary of Bobby's death, Kim quarrels with Jimmy over her visitation with Joey and confronts a female gang during a call; and Doc is visited by the father of a former patient whose debilitating injury may have been caused by Doc's error during treatment.

When a doctor comes to New York to search for the missing daughter of her drug-addicted sister, Faith and Bosco focus their attention on the child's stepfather, a New Jersey cop, after they discover that the girl was taken by a man in uniform; Tatiana returns home; Jimmy spends some quality time with Joey.

The crossover starts on ER S08E19 Brothers and Sisters

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

Doherty, riding on his motorcycle, is first to arrive at a multivehicle collision; Taylor is hit by a car; Tatiana goes to see Chevchenko, and tragedy ensues.

When a fire breaks out in the supermarket where Bosco and his mother Rose are doing some late night shopping, Bosco rescues most of the shoppers but cannot save a young mother when she goes back inside to retrieve her purse. After Jimmy tells him that the fire was probably deliberately set, Bosco is convinced that he saw the arsonist in the crowd outside after the fire. Sgt. Cruz gets Bosco and Faith assigned to the Anti-Crime Unit for a few days so that they can track the guy down. At the scene of another supermarket fire the next night, Faith takes down license plate numbers, Cruz photographs the crowd and cars at the scene, and Bosco nabs the man he saw in the crowd the night before. The man turns out to be a fire buff, but Faith and Cruz's work bears fruit and they find their arsonist -- the son of Doug Maple, an NYFD arson investigator. A depressed Sully is still on leave, drinking too much, and sleeping on the couch at Ty's and Carlos' apartment; Doc connects with an attractive

Monty and Joy hook up. Miguel witnesses one drug dealer murder another, and becomes the dealer's next target. On his first day back at work, Sully rides with Faith, who is put off by his short fuse and bad attitude. When he leaves a prisoner unguarded and uncuffed, Faith tells him to go home because he's not ready to be back on the job. Sully gets drunk and goes to his mother's nursing home. Sobbing about Tatiana, he tries to batter down the door when the receptionist won't let him in and calls the police. After Hancock arrives on the scene, Sully mouths off to him about Nancy in front of the other officers who are there to take him home.

Bosco is dismayed as he watches Cruz go to the extreme lengths of planting drugs, frightening children, and faking a dying declaration in their attempt to arrest the drug dealer who killed another dealer and then tried to to kill the 12 year old boy who witnessed the crime; Nancy tells Ty that she's ending her relationship with Hancock, and gives Ty the ammunition he needs to get out from under Hancock's thumb and back to duty at the 55, as well as getting Sully's suspension from duty lifted.

Sully's stopped drinking, but his poor attitude remains; Carlos gives his two week notice; a blizzard blankets the city and the squads are called in early; an understaffed Doc defies orders and puts Carlos back on the street as the squads are kept busy rescuing victims of the storm; Faith's initial wariness about Emily's new boyfriend Eric turns out to be well-founded when he is brought into Mercy after an overdose of Special K, but doesn't remember where he left Emily after she also got high; Faith, Bosco, Sully, Ty, Doc and Carlos go out to search for Emily, and rush her to Mercy after she's found in critical condition; Faith and Fred blame each other for letting Emily go out with Eric.

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.

Sully hits bottom when Ty washes his hands of the partnership after Sully's drinking goes completely out of control; a thief strikes fear in the hearts of the police when he phones in false ""officer-in-need-of-assistance"" calls to cover his fur store robberies; Faith and Maritza go at it after Maritza's lonesome cowboy tactics nearly get another cop killed, and Faith is forced to shoot a perp to save Maritza's life after she goes after the perp without backup; Doc has an unpleasant encounter with Joy's father; Faith is disgusted when she finds out about Bosco and Maritza, and Maritza confirms that she put Bosco in front of a lie about a dying declaration to obtain a conviction on a drug dealer; Ty overcompensates for Sully's inattention to the job by becoming a ""supercop"" with an eye to getting a gold shield.

Faith rebuffs Bosco's attempt to apologize for lying to her; the fire squad extricates a driver impaled after crashing into a store; after Doc makes an impassioned defense of Carlos before the review board, a re-energized Carlos goes back out on the street; Sully's job performance continues to decline as he neglects to keep an eye on a woman he was supposed to be guarding, and she snatches her critically ill baby from Mercy's E.R.; after they discover that the woman is mentally ill, Ty takes a multi-story tumble while trying to prevent her from jumping off a roof with the baby; Faith is stunned when an initially reluctant Emily is eager to continue visiting a drug counselor; Ty catches Sully drinking in the R.M.P. and seeks advice from a union rep; Carlos loses his job as part of the department's settlement with the West family.

Bosco and Faith chase after people who have stolen money from a crashed armored van. Kim meets a journalist. The girl who accused Carlos attempts suicide, and the truth comes out.

Distraught over losing an appeal to her suspension, Sasha gets into a car accident that claims the life of a young child; Sully and Ty take the L.S.A.T.; tensions flare between the cops and the firefighters when Maritza goes after J.D., the newbie firefighter, who turns out to be an ex-cop who ratted out Maritza's former partner for stealing drug money; Faith and Fred are still at odds over her return to work; Walsh is promoted to lieutenant; Ty watches over a devastated Sasha, who's racked with guilt over the car accident, Doc's shooting spree, and the events surrounding the deaths of Tanzi and Nardo; J.D. gives Faith and Bosco important evidence he discovered as he put out the fire resulting from Sasha's car accident, which leads the cops to uncovering the basis for the accident and exonerating Sasha.

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.

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

Everyone in the 55th Precinct faces their worst fears when terrorists are discovered to possibly be building a dirty bomb. Carlos and Levine face trouble in their relationship. Captain Finney decides to end his life, rather than surrender himself for the murder of Ty Davis Sr. Brendan and Davis try to cover it up.

Cruz teams up with Rice to track down the terrorists associated with the possible dirty bomb.

Monroe and Bosco deal with an angry mother on welfare who shoots up the welfare office, Davis and Finney stake out a man and take down a prostitution ring, Faith deals with Emily, Cruz and Monroe recieve bad news about their health.

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.