The episode opens with a scene from two weeks ago, where Mama Bartowski has a doctor perfecting a toxic spray. She then calls Chuck in present day and asks him to meet with her.
Chuck goes to meet his mom and he brings Sarah. Mary wants to set up a meet between the toxic gas doctor and Chuck posing as a weapons buyer. Chuck and Sarah decide to keep Beckman out of the loop and made it look like the meeting was their idea.
Chuck, Sarah, Casey and Morgan go through with the deal, but Mary comes by and breaks it up. She lets the doctor know that Chuck is CIA and then shoots him in the bullet proof vest covered chest.
Morgan has a lot on his plate as manager of the Buy More and helping out with the CIA, so he takes Big Mike's advice to delegate some responsibilities. He gives Jeff and Lester the job of setting up the Buy More for Halloween.
Mary takes Chuck to the lab where the doctor had the toxic gas. After knocking the doctor out and letting Chuck and the CIA save the day, she takes off once again.
The gas is let out inside of Castle and Chuck is exposed. He freaks out, while the doctor is fine because he has learned to be immune to the gas. Chuck gets him into the Aisle of Terror and Jeff and Lester's freaky pictures make the doctor go crazy.
Chuck and Mary set up a meet with Ellie so that the two ladies can see each other before Mom goes back undercover, but Casey and Sarah grab Mama B before it takes place. They steal her because they found out she actually was a double agent.