At the start of the episode Sarah, Chuck, Ellie, Captain Awesome and Morgan are playing a game while someone watches from outside. Sarah is back at home and about to take a Shower when she sees a reflection, she soon battles a ninja who she finally recognizes as old pal Carina, a stunning DEA Agent. Carina tells her that she is only in town to steal a diamond with Sarah's help.
Chuck sees her at the courtyard and flashes on her; he then burst in to Casey apartment where Casey and Sarah are talking to the General and Graham, who then want to use Chuck to get the diamond. The General orders them to get the diamond from opium financier Peyman Alahi's heavily guarded Malibu compound and hand it over to the NSA. Sarah then introduces Chuck to Carina, Morgan is instantly smitten about her. Carina shows up at the Buy More, Morgan ask Chuck to get him a double date with her.
On the double date, Chuck wants to watch a movie, but Morgan wants to talk so he can get to know Carina, Chuck later mentions that Carina just got back from Argentina, and everyone shuts up. Chuck gets a call from the Nerd Herd emergency Line. Chuck goes to the emergency only to find out it was Carina who called him, Chuck then gets nervous as Carina tried to Seduce him, and she then tells him about Sarah and Bryce Larkin being a couple.
The next day Sarah briefs him on the mission, they soon set off to Peyman's seaside mansion to steal the diamond. Sarah tells him not to trust Carina and that she had to get her out of trouble while in Pakistan. Carina breaks in through the bedroom; they find the Diamond in a protected chamber. Peyman and his goons find Chuck, Sarah and Carina. Sarah then lures Peyman into the hall; Chuck then gets a flash on the Diamond and warns that it is charged with 40,000 volts. She needs compressed air to get the Diamond; Carina then grabs the fire extinguisher and sprays the diamond off its pedestal. Chuck manages to grab it.
Chuck, Sarah and Carina escape, no longer trusting Sarah because he knows she lied about not dating Bryce, he tosses the diamond to Carina who escapes on a hidden Jet Ski. Sarah is annoyed. Casey has a tracker on Carina's phone and goes to track her down the hotel. While at the Hotel Carina bumps into Morgan, she sees Casey and soon drops the Diamond in Morgan's bag and tells him that it would never have worked out between us. Casey goes through Carina's hotel room looking for the Diamond; she soon seduces him and leaves him tied up in the room.
Sarah tells Chuck to stay at home while she goes to help out Casey; she finds him but no sign of Carina. Chuck and Morgan are playing on the X-Box when Morgan tells him to get a new game out of his bag, he finds the Diamond and has another flash, and realizes that the diamond belongs to an Afghani terrorist group. Sarah is being held hostage by the terrorists. They force her to call Chuck, asking him to find Carina and bring the diamond to the hotel, since they think that she still has the diamond. A ninja attacks Chuck but he soon recognizes it's Carina. She wants the diamond, but doesn't want to help Sarah, so Chuck reminds her that Sarah saved her life in Pakistan.
Carina goes with Chuck to help Sarah at the Hotel but they are surround by Peyman's goons; however, after exchanging a few words in a different language, the girls fight all the goons. Chuck has the Diamond - he packs it and sends it through the mail chute; Casey comes in and takes out the last goon. The General congratulates the team, Carina says her good-byes.
As she says goodbye to Chuck, she confides in him that she can tell that her old friend, Sarah, is actually smitten with Chuck. He is surprised but hopeful.
Chuck later brings over Pizza to Sarah's; he apologizes for his behaviour on the mission. He brings a vegetarian pizza without olives because that is the only true thing he knows about her so far. He tells Sarah that he wishes he knew one true thing about her that mattered, like her name, or her birthplace, or even her middle name; she says her middle name is Lisa, but Chuck doesn't seem to it hear.