Eddie is getting out of jail on parole.
Intelligence investigates a robbery/home invasion. Gas was used in the house to keep the family from waking up.
LIndsay suspects the daughter was sexually assaulted.
Lindsay traces the nitrous to a dealer and they bring him in. He tells them he got the tanks from a guy at a party.
They have the dealer throw a party to lure the guy out. He runs, but Halstead catches him.
There's a second home invasion and another girl who was raped. She saw their faces. The guy from the party wasn't one of them and they let him go.
Lindsay goes to speak to Tawny to have her look at pictures. Halstead discovers she's involved with Spence, the guy from the party that they let go. Lindsay is attacked and knocked out.
Halstead comes to her rescue before she can be raped, shooting the guy holding her hostage.
Tawny and Spence are arrested.
Halstead makes Lindsay promise never to go in without back up again.
Voight has dinner with Eddie and his new girlfriend.
Platt and Mouch talk to her father about the funds for the wedding and learn that he's broke. They're on their own for paying for the wedding.