Chuck's latest mission has him raiding a Malibu mansion to grab a million dollar diamond being used to fund terrorism. Tagging along is an attractive but less-than-trustworthy DEA agent.

Chuck gets a new mission when Sarah's best friend Carina comes through town with her fiancé Karl. Things get complicated when Chuck wants to hash out his and Sarah's relationship problems while they're on the mission. Meanwhile, Morgan finds himself in trouble when he lies to Jeff and Lester.

Chuck surprises Sarah with her old spy team, The C.A.T. Squad, leading to a mission in Rio. As The C.A.T. Squad works to settle a score with Augusto Gaez, old secrets and grudges come to light. Back at the Buy More, Morgan fends off the advances of Carina, a former flame and frisky member of The C.A.T Squad.

Before he can kiss the bride, Chuck must enlist his wedding party to take down Vivian Volkoff and stop her from destroying the big day. When he turns to Alexei Volkoff for help, the CIA sends its toughest agent, Clyde Decker, to stop them.