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.

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.

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.

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.

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.

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 Boston Marathon turns into a crime scene when a shooter begins targeting runners. Racing to catch the killer before another shooting, Jane and Maura must conduct their investigation in secret so as not to cause a mass panic.

Jane was once abducted and neared killed by imprisoned serial killer Charles Hoyt. Now a body found in a park has all the indications of being his work. Jane must do her best to keep her fear of this man in check while Maura attempts to get inside the mind of the killer.

Jane's investigation of a murdered identity thief leads her to Boston's Irish-mob past. After startling new information, the victim leads Maura on a personal quest. On the home front, Frankie Jr. attempts to help his father find some new clients for his plumbing business.

After an undercover cop working a narcotics-smuggling sting is shot dead, the killers next turn their sights 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. On the home front, Jane's parents are excited that their oldest child, Tommy, is being released after serving time in prison.