Leonard comes up with a great idea for an phone app and the guys all pitch in to help. When Sheldon becomes too controlling, Leonard fires him. Penny finds Sheldon by himself in the hall, she invites him to work with her on an app of their own. Quickly annoyed with him, Penny begs the guys to take Sheldon back. When they refuse, she convinces Sheldon to practice his sarcasm and apologize to Leonard so he can work with them again.