From among thousands of sailors in Boston during Fleet Week, an unknown sailor is suspected of two rapes and murders. Admiral Frost appears and he and his son Detective Frost do not see eye to eye. Policeman Rizzoli Jr. plays a part.

After her boyfriend Casey Jones is unable to get to Boston, Jane takes Maura to her dreaded high school reunion. She hates most of the people there but one former classmate that she liked, Steve Sanner, says he would like to discuss something with her. Before he can do so however, Steve is shot and killed while taking a walk on the football field. The killer used a steel wool-filled water bottle as a silencer. He worked for another high school classmate, Rory Graham, who says he wasn't having any trouble at the office or with co-workers. Based on his phone records, they suspect he may have been having an affair with another former classmate, Debbie Tibbet, but when she is found dead her husband tells the police she had recently become very secretive. A third dead classmate gives them the clue they need to identify the killer. Meanwhile Vince Korsak's ex-wife is back in town wanting money for a new enterprise. Vince would like to see his 16 year-old son Josh.

Jane looks for a way for Maura to meet her biological mother, Dr. Hope Martin. Angela gets involved in a political campaign. And a nun from Jane and Frankie Jr.'s past returns.

The squad gets involved in an incredibly dangerous scenario when a horrifying incident occurs during a drag race; Jane gets a lead that points to drug trafficking being the motivation for a murder; an investigation is hindered.