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.

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.