In the wake of the World Trade Center disaster and Danny's disappearance, the 15th Precinct faces a gruesome investigation when four young girls are found dead in an apartment. Sipowicz, in a black mood because his partner's whereabouts are still unknown, takes out his anger on everyone around him. While investigating the murders, Sipowicz and McDowell team up with a young narcotics officer, John Clark. When a possible lead in Danny's disappearance emerges, the trail leads right to the son of a Mafia capo. When the worst possible news is confirmed, a witness is enlisted to wear a wire as they go after the suspect. As Medavoy, Jones and McDowell learn the quadruple murder was a robbery gone bad, Sipowicz once again confronts the temptations from the past, anticipating the next day's undercover operation.

After the funeral of his old partner, Danny, Sipowicz returns to the squad room and is abruptly teamed with his new partner, John Clark. Clark's father, John Clark, Sr. — Sipowicz's old nemesis at another precinct — butts heads with both Sipowicz and Clark Jr., when he interferes with their first case together, the mysterious stabbing death of a wealthy woman. Meanwhile, McDowell and Jones discover a vintage '56 Les Paul guitar is a key piece of evidence in the death of a young, struggling musician, and leads to the victim's own jealous roommate.The tension between Clark, Jr. and his father rises when Clark, Sr. crashes the 15th's toast to Danny.