A community parade turns deadly in a case that brings family tensions and politics to the forefront. Maura, who is dealing with her own family issues, is not quite herself. And a surprise visit from Lt. Col. Casey Jones reveals some shocking news.

Jane is unhappy when a former colleague returns as the new lieutenant of the drug unit; a tip from Cailin causes Maura to investigate Hope.

A body is discovered in the church at TJ's christening; Jane almost abuses her power to protect Tommy; Lydia's fiancé threatens to take custody of TJ; budget cuts cause tension at the department.

Maura becomes the key suspect in a homicide case when Maura’s date turns up dead – and Maura can’t remember their evening together. As the shocking evidence against Maura piles up, Jane struggles between protecting her best friend and doing her job.

On the first day of Paddy’s murder trial, Maura gains insight into her father from Hope. Korsak opens up about Cavanaugh’s tragic past. And in an unexpected twist, Maura must decide which side she’s on when she and Jane unravel a shocking secret about Paddy and Hope that affects them all.

A popular high school teacher is killed in a hit and run that is clearly no accident. The squad works to solve the case, but Jane is preoccupied with Lt. Martinez’s apparent favoritism towards his own drug unit.

Frankie Jr. is brought in to help with a gruesome murder case involving a youth hockey league. Frustrated with Hope, Cailin asks to stay with Maura. But Maura quickly learns that living with a teenager requires skills she does not have.

When Jane and Maura are asked to present the case of serial killer Charles Hoyt at a symposium for law enforcement, Jane worries that her greatest challenge will be facing bad memories. However, as she and Maura begin a simulation of investigating Hoyt’s murders, they soon come across a horrifying discovery. In a matter of moments, the team finds themselves drawn into a lethal game of cat and mouse with a new and terrifying serial killer.

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.

A mock trial advisor dies during a competition. Meanwhile, Jane is concerned that Angela may be hiding financial issues.

The squad rushes to solve a violent homicide case muddied by conflicting evidence. Maura is burdened with the major decision of whether to take in her recently paroled grandfather. Meanwhile, Jane and Casey are forced to decide between their careers and their romantic relationship.

A kidnapper dressed as a clown re-emerges after 20 years; Jane's relationship with Casey grows more serious; Maura inadvertently gets in the middle of another relationship.

A musician is stabbed in a bar; 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 poisoning; Tommy announces some big plans; Maura's birth mother tries to make amends with her daughter.

A senator's daughter is found murdered; Tommy begins to slip back into old habits; Jane reveals some shocking news.