15 Division throws Sam and Andy a engagement party at the Black Penny. Sam asks Oliver to be his best man. Andy loses her engagement ring. Later, she finds out that Sam has had it all along and he’s but an electronic finder on it that quacks like a duck so she won’t lose it again. 

Commissioner Santana confronts Noelle about assigning Juliet Ward from Internal Affairs to 15 Division. He’s angry because he wasn’t informed. He wants a report by the end of the day. Noelle tells Sam that the only suspect they have right now is Oliver. Sam is worried that if Santana is dirty he will happily pin the bombing on Oliver to cover his tracks.

Sam and Andy pull Dov into the investigation. He tells them about Chris Klem who sold the explosives but he and his daughter have disappeared. When they eventually find Chris and Ava, they are on the run and in fear for their lives. Chris says he sold the explosives to to a cop who was in a hurry and didn’t finish the paperwork. When he began to ask questions after he heard about the evidence room bombing, his daughter was threaten so they ran. When asked for the name of the officer who bought the explosives, he says it was Oliver Shaw.

Oliver is riding a high after finding a missing autistic boy, when Sam and Andy tell him what is happening. He almost breaks down, realizing that he could end up in prison for something he didn’t do. 

Track picks up Chris and Ava Klem to transport them to a safe house. On the way, her cell phone rings and Steve’s picture shows up on the screen. Chris Klem freaks out when he sees it. That’s Oliver Shaw, the man who bought the explosives!