Jane and Maura find themselves submerged in the cutthroat, high-stakes world of competitive bass fishing when a tournament-leading fisherman is killed. At the same time, Frankie is paying the price after losing a bet.
When it appears one of their own shot an unarmed man on a Boston subway platform, the team must find the real killer while clearing their detective's name.
The murder of a crime tech shocks the team; Maura is suspended from her position; Jane is determined to catch the killer and clear the department so Maura can be reinstated.
An investigation into the death of a jeweler leads to a member of the Isles family; Maura has been keeping a secret.
When a state trooper is killed in Maine, the getaway car is traced back to the mastermind of the attacks on Jane.