Shortly after sailors invade the streets of Boston for Fleet Week, a young girl is found dead. Frost's father, a Navy Admiral, comes to town, causing tension with his son. And, Maura goes on a date with Angela's mechanic.

Jane attends her high school reunion and brings Maura along for the ride, but the fun is cut short when one of her old classmates turns up dead on the football field. Jane must focus on the past when she realizes everyone in her class is a potential suspect. Meanwhile, Korsak gets a visit from ex-wife Melody Patterson (guest star Lolita Davidovich), who hopes he’ll invest in her new business. Chris Vance returns as Sgt. Major Charles “Casey” Jones, an old flame of Jane’s, and Matthew Del Negro guest-stars as Angela’s car mechanic, Giovanni, who once had eyes for Maura.

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

When a late-night amateur drag race turns deadly, the squad works quickly to solve what turns out to be a particularly dangerous case. As evidence unfolds, Jane suspects that the motive for murder may have been an attempt to conceal drug trafficking. However, when she turns to Lt. Martinez for help he seems to be thwarting her investigation.