Melissa Rauch

Penny asks Leonard to lie to her father, Wyatt (guest star KEITH CARRADINE), while Howard, Raj and Bernadette pull an all-nighter at a telescope.

While Sheldon and Koothrappali attend a university mixer, Leonard is upset to discover that Penny believes in psychics. Danica McKellar (The Wonder Years) guest stars as the object of Raj’s attraction.

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

Sheldon takes on his greatest challenge when he attempts to help Penny understand physics, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

Amy finds she has sexual feelings for Penny's ex, Zack (guest star BRIAN THOMAS SMITH) while Koothrappali and Wolowitz try to prove who would be the better superhero.

Suffering from a case of "physicist's block," Sheldon's search for the answer to a physics problem leads him to work at the Cheesecake Factory with Penny.