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.
- Angie Harmon as Detective Jane Rizzoli
- Sasha Alexander as Dr. Maura Isles
- Jordan Bridges as Detective Frankie Rizzoli, Jr.
- Lee Thompson Young as Detective Barry Frost
- Bruce McGill as Detective Vince Korsak
- Lorraine Bracco as Angela Rizzoli
- Brian Goodman as Sean Cavanaugh