Leonard is torn between being honest or self-serving when Stuart asks his advice for an upcoming second date with Penny. Wolowitz realizes there's a crucial error in a toilet he designed for the International Space Station.
Leonard and Raj take Wolowitz to Las Vegas to help him get over his break-up with Leslie. Sheldon, home alone and looking forward to it, locks himself out and has only one other place to stay—Penny's.
The gang is thrilled when they see Terminator: The Sarah Connor Chronicles' Summer Glau is also aboard their train to San Francisco for a scientific symposium. Meanwhile, Sheldon frets over having forgotten a paper he wants to present to George Smoot.
Penny's criticism of Wolowitz's romantic life pushes him into depression and AWOL for a fighting robot battle the rest of guys are depending on him for.
Leonard seeks Penny's counsel when his relationship with Stephanie takes off faster than he'd like. Sheldon's hypochondriac tendencies get the better of him.
When Sheldon bans Penny from the apartment for numerous minor infractions, she decides to retaliate. Howard and Raj search for the America's Next Top Model house.
Penny opens up to a reluctant Sheldon after a less-than-stellar first date with Leonard, placing him in the uncomfortable position of having to keep a secret.