Chuck is not happy with Sarah after she ruined Ellie's reunion with her mother. Chuck rehearses the fight with Morgan, who is dealing with a fight of his own, with Casey. Per Chuck's advice, Ellie goes on a search for anything left over from their father. She looks through the classifieds and finds and ad for an old Ford Mustang which catches her eye.
Chuck is determined to prove his mother's innocence. He sneaks into Castle to talk to her. He meets her handler, Tuttle. At the tavern, Chuck has Morgan go in to see what is going on. He ends up dropping his earpiece into a glass of water and spends a lot of time in the bathroom trying to dry it off. While Morgan is in the bathroom, Chuck goes in and meets Tuttle. They are both shot with tranquilizer guns by Volkoff's team.
Morgan, Casey, and Sarah go to Chuck's mom for help. She agrees, but wants to meet with Ellie in return. Ellie is shaken up by the reunion. Her mother reveals a story of an old Ford Mustang, the same one she saw in the fieds.
Chuck and Tuttle end up at a bank. They get two disks, as do Sarah and Chuck's mom. These disks are special to fit a computer in Chuck's father's research lab. These disks may prove Chuck's mom's innocence. While working together to take down assassins, Chuck and Sarah resolve their fight. Tuttle gets shot and the rest escape to Chuck's dad's facility. Chuck and Morgan make up as well. They find a bloodstain where Tuttle was shot.
Chuck and Sarah load the disks and nothing was discovered. Tuttle shows up, knocks out Sarah, and reveals himself to be Alexei Volkoff. Chuck and Sarah are tied up while Volkoff and Chuck's mom set up the room with explosives. Before leaving, Chuck's mom slips Sarah a razor to help the escape, and she tells Sarah to protect Chuck. Chuck and Sarah manage to escape seconds before the explosives went off. Ellie tells Devon about her mother's message and they go track down the Mustang. In the car, Ellie finds a note written by her father saying that he has given her the car for a reason and that she should know what to do with it. Something mysteriously glows in the car as they drive away.