Tensions are high as the squad investigates a possible copycat of the legendary Boston Strangler…or could it be the Boston Strangler himself? Meanwhile, Jane butts heads with her new boss, Lt. Grant, who just happens to be from the same neighborhood where Jane grew up. And Maura gets into trouble with her habit of diagnosing everyone – including her date.

An investigation leads Jane into Boston's checkered past when an identity thief is murdered; Maura goes on a personal quest.

Tensions continue to mount between Jane and Maura, causing those close to them to be caught in the middle. But they must put aside their differences when they investigate the case of a college student who died in a tunnel. Meanwhile, Frankie Sr. returns with news that upsets Angela.