After Liz asks Mike to look into the death of the girlfriend of her fireman friend Nick, Mike comes into conflict with Nick's boss, who's an old nemesis; Marcellus works the case from a pattern-killing angle, linking it to a similar murder 2 years ago, and discovers that the otherwise unconnected victims had the same locksmith; Mike discovers that a fire that Nick's squad recently fought was in a building that housed a methadone lab where $112,600 disappeared, and suspicion points to the squad.

Mike uncovers an illicit adoption ring trafficking in stolen babies when he grudgingly agrees to help one of Liz's clients, a former addict who's turned her life around, in the search for her missing child; Marcellus calls an end to it when he realizes that his obsession over the new man in Deborah's life has gone too far.