Chuck and Sarah’s wedding prep includes one final detail: ensuring that the mother-of-the-groom makes it to the ceremony alive. Meanwhile, Morgan’s responsibilities as Best Man include his most dangerous mission yet, as he faces Vivian Volkoff. Elsewhere, Ellie tends to the last details of the rehearsal dinner and seeks help from an unlikely source.
Chuck is put in charge of a top-priority mission, but his leadership skills are pushed to the limit when there is a murder in Castle. Meanwhile, Awesome takes on a mission of his own when Ellie finds an alarming new hobby. Elsewhere, Morgan's leadership is also tested when his Buy More troops wage war against Large Mart.
Valentine's Day is interrupted when Chuck and the team are sent on a mission to England to protect a reclusive young heiress, Vivian McArthur. Meanwhile, Casey gets an offer from the mysterious Jane Bentley. Back at home, Ellie and Awesome find an unlikely solution to a parenting problem, as Morgan ponders a big move.
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.
The mission to take down Volkoff reaches a dangerous new level, while big changes loom at home. As Sarah works to free Chuck’s mom, Chuck and Morgan embark on their own mission to take down Alexei Volkoff. Meanwhile, Casey bonds with his daughter, Alex, while Ellie tries to ease Awesome’s anxieties over fatherhood.
Sarah takes dangerous measures to help Mary Bartowski bring down Alexei Volkoff, as Chuck worries that she may be getting in too deep. Sarah, though, must enlist the help of Chuck, Morgan and Casey to complete her undercover mission. Meanwhile, Ellie and Awesome are at odds over what to name the baby.
Chuck and Sarah's romantic mission is canceled with the arrival of Hugo Panzer and Heather Chandler. But Chuck grows more interested when the manipulative Heather claims to know a secret about his mom. Meanwhile, as Morgan prepares the Buy More for a huge video game release, he gets a surprise from Big Mike.