The Big Bang Theory: Season 4

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

Leonard keeps an affair a secret from Sheldon, Howard and... More Raj.

Sheldon's answers during an FBI interview put Wolowitz's security clearance... More in jeopardy.

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

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

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

The guys find a "super" use for Penny's new boyfriend,... More Zack, when they enter a costume contest as the Justice League.

Leonard's idea for a smartphone app derails his friendship with... More Sheldon.

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

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

A wealthy donor to the university makes Leonard consider how... More far he's willing to go for the sake of science.

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

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

Sheldon is baffled by Wolowitz's magic trick. Meanwhile, Leonard realizes... More dating Priya may make it impossible to continue being friends with Penny.

Sheldon's online-game account is hacked by Todd Zarnecki, who then... More proceeds to steal all his items prompting the guys to go on a quest to retrieve them. Penny, Bernadette and Amy discuss how Penny groomed Leonard to be willing to try various things and more adventurous boyfriend... for some other woman — Priya.

Sheldon and Amy decide to start several rumors about the... More others as a test. Meanwhile, Howard takes his relationship with Bernadette to even higher level.

When Leonard spends too much time in the shower with... More Priya, Sheldon charges Leonard with two violations of the roommate agreement. However, before he can get too far, Priya uses her skills as a lawyer to nullify the charges due to the agreement's vague wording, much to Sheldon's dismay. When the guys take advantage of Priya's skills in order to eat Greek food on pizza night, Sheldon goes to Penny, who invites him to a girls' night out with Amy and Bernadette, which Sheldon agrees to after Penny mentions that they may be talking trash about Priya. After the girls drink some cocktails, they decide to take Sheldon dancing, which Sheldon reluctantly goes along with. After dancing, Sheldon takes an intoxicated Amy back to her apartment and as well as talking about Priya, meets a monkey who is addicted to smoking cigarettes. Amy tells Sheldon not to give in to Priya's law skills, before kissing him and going to her bathroom to vomit.

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

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

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