Pembleton and Bayliss have only twelve hours to grill their prime suspect in the Adena Watson case before they must let him go.

The homicide team pulls the graveyard shift on the hottest night of the year. Bayliss is consumed by the Adena Watson case, driving a bigger wedge between him and partner Pembleton. Giardello finds a baby in a cage. A renegade Santa Claus runs loose in the building and the whole squad tries to figure out who's responsible for a candle that keeps getting lit.

Lewis and Crosetti uncover a woman who's been killing her husbands for insurance money. Howard tries to keep her cases-solved record perfect, but she is reassigned with Felton as her partner. Bolander convinces Munch to help him finish up an unsolved case. A new guy, Tim Bayliss, from the mayor's office gets his first case in homicide, the murder of an 11-year-old girl. His partner Pembleton, we find out, is less than enthusiastic to work with him or anyone else in the unit.

Howard and Felton are in court over the Pony Johnson case, Crosetti and Lewis go head to head with the Secret Service and Bolander and Munch argue over drug legalization. Meanwhile, Pembleton gets an unexpected job offer.

Bayliss and Pembleton continue to struggle with the Watson case. Bolander and Munch discuss ""iguana style"" and are called to check out the homicide of a victim that isn't dead, at least the first time they're called. While checking out some leads for the Watson case, Crosetti gives his theory on the conspiracy to kill Abraham Lincoln. Lewis wants to flood Memorial Stadium. Bolander expresses an interest in Dr. Blythe; Munch advises and sends flower's in Stan's name. Danvers needs a stronger case; however, Howard is frustrated with a dead end. Then the ghost of the victim leads her to the undiscovered proof. Tim attends Adena's funeral.

Crosetti focuses his investigation into the shooting of Officer Thormann on one suspect, while Lewis continues to investigate. Meanwhile, Pembleton and Bayliss pursue different leads in the murder case of eleven-year-old Adena Watson.

Crosetti and Lewis investigate the shooting of a fellow police officer whom Crosetti regards as a son, Howard suspects a rabid Spiro Agnew fan of murder but ends up solving the Calpurnia Church case meanwhile Bolander makes a friend whose death interrupts his date with Dr. Blythe.

Quitting smoking dominates the conversation ad behavior of the homicide detectives even as they solve what may be a gang-related killing of a 14-year-old boy. Lt. Giardello discovers a secret asbestos removal project on the third floor and confronts his superiors on behalf of his squad.

While Giardello is busy sending off an old friend to retirement Pembleton and Bayliss investigate the murder of a dog, Howard and Felton argue over whether Felton finds Howard attractive while dealing with a drug-related homicide and Bolander and Munch take Dr. Blythe's son on a ride along. Meanwhile, Crosetti takes care of the bed-ridden and blind Thormann.