Erin faces off against her ex-husband in court when he represents the person she is attempting to convict of murder. Frank is confronted by a mother who accuses the NYPD of being negligent in solving her son’s murder. Jamie rides with a new partner.

When the team intercepts a terror group's message meant for Murdoc, Mac poses as the psychopath to save the intended target and find out why they want Murdoc to assassinate him.

As Mary’s upcoming wedding looms, a terrible tragedy pushes Mary and Darnley apart, forcing Mary to enlist in Catherine’s help. Elizabeth encounters a traitor to Spain, who petitions her to support an expedition to the New World.