A Revolutionary War re-enactment becomes the scene of a real killing when a soldier turns up dead. Maura's extensive knowledge of American history becomes important as she and Jane try to solve the case. And Maura's brilliant mother, Constance Isles, comes to Boston for an art exhibit.

A serial killer claims to have clues about the murder of another prisoner; Frankie Jr. prepares to take the detectives exam.

Jane and Maura’s friendship suffers following the shooting of Maura’s biological father, gangster Paddy Doyle. Jane also finds herself in the middle of an Internal Affairs investigation. And her relationship with Agent Dean is exposed.

Maura becomes the key suspect in a homicide case when Maura’s date turns up dead – and Maura can’t remember their evening together. As the shocking evidence against Maura piles up, Jane struggles between protecting her best friend and doing her job.