After an undercover cop working a narcotics-smuggling sting is shot dead, the killers next turn their sites on Boston homicide headquarters, leaving Jane, Maura and Frankie Jr. trapped in a fight for survival on their home turf. It's a situation that will force Maura to challenge herself like never before.

When an identity thief with no apparent identity of his own is found brutally murdered with an ice pick, the investigation leads Jane into Boston's Irish-mob past. A startling discovery about the victim sends Maura on a deeply personal quest. Meanwhile, Frankie Jr. tries to help his dad add to his client base.

A body discovered in a park appears to be the work of Charles Hoyt, the imprisoned serial killer who once abducted and nearly murdered Jane. As Maura tries to get inside the mind of the killer, Jane struggles with keeping her fear in check.

A marathon turns into a moving crime scene when a shooter begins targeting runners during the race. Jane and Maura, who had planned to compete in the race, instead find themselves racing to catch the killer before another runner goes down. The crowded and impassable city forces Jane and Maura to conduct their investigation on the ground and in secret so the hundreds of thousands of spectators don't become casualties of a mass panic.

Jane and Maura investigate what appears to be a hate crime, the brutal assault and murder of a woman leaving a lesbian bar. With Jane going undercover, they hope to lure the killer out in the open. Off the job, Maura hooks Jane up with a handsome yoga instructor.

The eldest brother in a Boston "Brahmin" family (direct descendents of passengers on the Mayflower) is found in the harbor dead after an apparent sailing accident. But Maura's close connection with the family and Jane's resentment over the wealth they display threaten to derail their investigation. Angela, meanwhile, tries her hand at selling a Polynesian health drink.

After a student is gunned down in broad daylight, the investigation reveals she had more than a few secrets. Meanwhile, Jane's mother Angela gets into a spat with her father over the car.

Jane and Maura investigate the mysterious death of a young boy whose family is from Cape Verde. It appears at first that he may have died during an attempted exorcism, and it may take a message from beyond the grave for Jane to pinpoint exactly what happened. Jane is distracted from the case when her mother sets her up on a surprise date.

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.

Detective Jane Rizzoli and medical examiner Maura Isles investigate the grisly murder of a wealthy couple. The M.O. matches the work of a serial killer known as the Surgeon, who once nearly murdered Jane. Now that the Surgeon is behind bars, it seems one of his proteges is picking up where he left off.