Jimmy's spirits are low when Sabrina's relationship with Wyatt becomes serious, so Virginia and Burt convince him to create a make-believe girlfriend to make her jealous. Barney invites Jimmy to his improv class, where he meets Mary-Louise (guest star Ashley Tisdale) who agrees to play along with his plan to win over Sabrina. But when their acting becomes too convincing and Sabrina falls for their fake relationship, all plans might backfire on Jimmy.