Penny goes on a date with Sheldon's robot — well, with Sheldon operating a telepresence robot. Howard and Bernadette get closer.
Sheldon tries to extend his lifespan through extreme health measures. Leonard adjusts to life post-Penny breakup.
Sheldon replaces Penny with 25 cats after she and Leonard split. Amy Farrah Fowler is mentioned and will soon change everything.
Howard's secret online gaming life is exposed by Bernadette. Raj deals with a romantic situation involving a fantasy game.
Leonard is desperate for a girlfriend and takes a questionable approach to dating. Sheldon and Amy's strange courtship continues.
Howard lies to Bernadette about something from his past and the deception comes back to haunt him. Raj plays wingman.
Sheldon must apologize to Kripke to get access to a computer he needs. Saying sorry might be the hardest thing he's ever done.
The guys camp out for movie tickets and encounter a bully. Indiana Jones and the issues of nerd culture collide.
Penny's dad visits and Leonard tries to impress him. The father-boyfriend dynamic gets complicated when Penny isn't sure what Leonard is.
Amy and Penny deal with unexpected physical attraction — not to each other. Sheldon is baffled by the biological response.
The guys dress up as the Justice League for New Year's Eve. The costume planning alone takes up most of the episode and it's glorious.
Leonard comes up with a smartphone app idea and the guys work together to develop it, but creative differences cause friction.
The gang goes on a couples' retreat at a science conference. Sheldon and Amy's relationship evolves while everyone else's gets tested.
Raj teaches Sheldon acting techniques for a lecture. Penny starts taking college classes, and Leonard supports her academic ambitions.
A university donor flirts with Leonard, and he's torn between personal discomfort and professional obligation. Sheldon has no such dilemma.
Bernadette moves in with Howard, much to his mother's dismay. The Wolowitz household dynamics shift dramatically.
Sheldon starts his own social group and Leonard isn't invited. The rival friend group creates apartment tension.
Sheldon is tricked by a magic trick and becomes obsessed with figuring it out. His pursuit of the secret is relentless.
Sheldon's World of Warcraft account gets hacked and the guys mount a real-world mission to confront the hacker. Justice, nerd-style.
Amy and Bernadette spread gossip about the guys and it gets back to them. The rumor mill reveals some uncomfortable truths.
Sheldon's roommate agreement is challenged when Priya finds legal loopholes. The power shift in the apartment is dramatic.
Penny secretly auditions for a role and worries about the guys finding out. The gang investigates when she starts acting suspicious.
Howard proposes to Bernadette and Penny worries about Leonard doing the same. Raj makes a decision that surprises everyone.
Raj wakes up in a situation that changes his relationship with Penny forever. Bernadette accepts Howard's proposal. The season ends with shakeups.