In the season premiere, a community parade turns deadly and family tensions and politics arise. A surprise visit from Lt. Col. Casey Jones (CHRIS VANCE) reveals shocking news.

Jane and Maura investigate the death of a young woman who is found washed up on the beach. Maura confirms that she drowned and manages to trace the exact location by analyzing the water in her lungs: a tank in an old fish factory. Jane is somewhat upset to find that an old flame, police Lt. Rafael Martinez, is back in Boston. They had worked together in the narcotics division but their relationship ended after a confidential informant had been killed and Martinez left to join a special task force some 8 years ago. The dead girl is identified as Brenda Thompson, a journalism student who was pursuing a drug story on her college campus. When Jane finds Lt. Martinez's business card among her possessions, it seems that he was using her to get information. Meanwhile, Maura learns that she may be in danger owing to her father's activities.

Baby TJ's christening turns grim when a body is discovered in the church. Jane almost abuses her power in order to protect her brother Tommy (COLIN EGGLESFIELD).

Dr. Isles becomes the suspect in the murder of a mysterious guest of a charitable fund-raiser.

The decades-old death of a mother and child open a closet door revealing skeletons that threaten to complicate the start of Paddy Doyle's RICO trial.

A reclusive hoarder becomes the subject of an investigation into the murder of a city sanitation employee.

The hit-and-run murder of a high school science and driver's education teacher focuses on a group of friends who were also students of the victim.

"Sports rage" and angry hockey parents are the focus of the investigation of the murder at a youth hockey game.

When someone begins to stage copycat murders presented at a symposium on serial killers, detectives believe the suspect is one of the meeting participants.

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.

A mock trial advisor (A'DA ALISON WOOLFOLK) dies during a competition. Meanwhile, Jane is concerned that Angela may be hiding financial issues. DOUG SAVANT also guest stars.

Two puzzling murders share a surprising link that could be the key to finding the perpetrators. Meanwhile, Jane and Casey come to a crossroad and Maura assumes caretaker for Patrick Doyle, Sr. who is being released from prison.

The Boston Police department is haunted from the past when a man in clown-costume almost kidnaps a little boy. Is it the same person that has molested and kidnapped boys in the 1980s?

A musician is stabbed in a bar and the squad realizes that the stabbing victim had something to hide. Jane's father returns with shocking news.

When a food truck chef dies suddenly, all signs point to a suspicious poisoning, but many questions remain unanswered. Meanwhile, Tommy announces some big plans that have Angela very excited. And Maura's birth mother, Hope, takes a bold step toward making amends with her daughter.

Homeland Security steps in when a senator's daughter is found murdered. The squad rushes to solve the case, which could put national security at risk. Meanwhile, Tommy and Frankie get into a fight after Tommy starts slipping back into bad old habits. And Jane reveals some shocking news that could change her life forever.