Dylan, having returned to teaching after helping the NYPD catch a serial killer, is called upon again to aid Detective Needham on a complex case involving the murder of a venture capitalist.

The murder of a young man who recently left his family's religious community leads Dylan and Lizzie to a series of possible suspects; Lizzie's younger sister unexpectedly drops by for a visit.

Dylan and Lizzie are assigned to a murder in Central Park after their investigation into a chemical attack on the subway is taken over by the FBI.

Dylan and Julian go under cover in a hospital to catch an "angel of death" who is killing patients who have non-life-threatening ailments; Lizzie asks Andy for his legal expertise when a personal trainer sues her for accidentally injuring him.