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.

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.

Singer and guitar player is brutally and mysteriously stabbed in a bar. As details emerge in the case, the squad soon realizes that the victim had something to hide. Meanwhile, Jane's dad returns after being gone for more than a year. And he's got some shocking news.

When a kidnapper who dresses as a clown reemerges in Boston after more than 20 years, the squad is struck with fear. Desperate for clues, they dig through files from the unsolved abductions of the haunting 1988 "Summer of the Clown." Meanwhile, as Jane's relationship with Casey becomes more serious, they are forced to face the fact that one of them will have to compromise if they are to take things to the next level. Maura also finds herself in a dilemma when she inadvertently gets in the middle of another relationship.

The squad rushes to solve a violent homicide case muddled 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.

Mock trial advisor dies tragically during a competition. Meanwhile, Angela's increased interest in selling brownies has Jane concerned that she may be hiding financial issues. And Tommy hires a lawyer to settle his claim against the Storrow Center.

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.

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.

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.

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.

When a beleaguered Jane spills hot coffee on a stranger at Boston Joe's, a viral video of Jane's bad day potentially jeopardizes her career and reputation. Meanwhile, the squad rushes to solve a puzzling murder case involving a conspiracy theorist.

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.

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.

TJ's christening turns grim when a body is discovered in the church. Jane almost abuses her power in order to protect Tommy when Lydia's fiancé, Stuart Stawbridge threatens to take custody of TJ, and budget cuts cause tensions to run high around the department.

While investigating the homicide of an overzealous journalism student, Jane is not happy when a former colleague returns to BPD as the new lieutenant of the drug unit. But the murder she's investigating soon forces her to deal with him - and the event that wrecked their relationship. Meanwhile, an alarming tip from Cailin causes Maura to investigate Hope.

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.