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 and Sarah suspect Casey is carrying out private missions. Chuck fears the CIA's new operatives will render him obsolete. Morgan settles in with a new roommate. Awesome becomes uncomfortable with Ellie's research.

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.