Guest Appearances

An embarrassing secret of Wolowitz's comes to light, while Sheldon and Raj have a small war at work.

Amy finds she has sexual feelings for Penny's ex, while Koothrappali and Wolowitz try to prove who would be the better superhero.

While the guys camp in line for a long-awaited movie screening, Penny and Bernadette invite Amy to her first slumber party.

Penny asks Leonard to lie to her father, while Howard, Raj and Bernadette pull an all-nighter at a telescope.

Hoping it will make him a better teacher, Sheldon has Penny give him acting lessons. Raj has fantasies about a friend's girlfriend.

Leonard realizes he’s the only one without a girlfriend, while Sheldon wants to get rid of his.

As Wolowitz contemplates taking things with Bernadette to the next level, Leonard rekindles his relationship with Raj's sister.

After overhearing that Wil Wheaton is entering a trading-card competition, Sheldon decides to enter it himself.

Sheldon becomes concerned when everybody begins to hang out at Raj's apartment and discovers Leonard is the center of the group.

Bernadette runs into her ex-boyfriend while attending a science event with Wolowitz.

Sheldon vows to destroy Kripke while Wolowitz tries not to destroy his new relationship with Bernadette.

Sheldon's World of Warcraft online game account is hacked and he is determined to find out who did it.

Penny gets help from Sheldon in order to understand what Leonard's work is, while Wolowitz develops a jealousy.

When Bernadette receives her PhD, Wolowitz feels emasculated. Raj and Leonard swap places and Penny does something she's regrets.

Sheldon and Amy decide to start several rumors about the others as a test.

Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.

Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.

Leonard is aghast to find out a secret of Penny's: she believes in psychics.

When Leonard spends too much time in the shower with Priya, Sheldon charges Leonard with two violations of the roommate agreement.

When Howard finally breaks the news to his mom that he's engaged to Bernadette, it lands her in the hospital.