-Professor Rhonda Clark is killed in her hot tub. Across town executive Mark Cabot is shot. The detectives work both cases.
-Rhonda got tenure at her school ahead of her husband but he has an alibi for her murder. Maura finds dog hair on the victims body but not from her dog. They eventually find the dog through a local dog park. It's walked by Mark Cabot's wife who made a "Stangers on a Train" type pact with Rick Clark to kill one another's spouses.
-When Paddy Doyle's father is released from prison after 30 years, Maura temporarily takes him in even though he never wanted her to be born. Casey points out that the old man is terrified to live outside of prison.
-Casey's home on leave and has been promoted to Colonel. He must decide whether or not to reenlist and tells Jane if he chooses not to, he wants them to get married. Jane doesn't know what to say.