Pat is rude to Casey as he informs him he knows about him sleeping with his wife. Casey tries to explain himself, but it falls on deaf ears as Pat goes on the war path against him.
After an apartment fire, Pat tries to pin all the blame on Casey after a someone is almost killed.
Casey protests his innocence, but Pat pulls Welch in on the plan, but Welch is reluctant. Pat blackmails him by saying he is done if he doesn't sign the paper confirming it. Welch refuses and leave Firehouse 51. Casey thanks him.
Donna wants Boden back at work so she can get a break with the baby. Boden is initially reluctant, but when he finally tells her he will be returning to work, Donna acts shocked and annoyed.
Brett pushes Dawson to date again and sets her up with a guy from Chicago Medical. they go on a double date with Brett and Cruz.
Mouch finds out that he has a son after the sperm donor clinic doesn't conceal his confidentiality. He gets ready to meet his son, but chickens out at the last minute. He then goes to the pub and tells Platt he met with him.