While Penny worries that dating Leonard has ruined her for normal guys, Wolowitz and Koothrappali search for Sheldon’s perfect match online.

Leonard tells Penny about how he met Sheldon for the first time…and what happened to the elevator.

Leonard and Sheldon compete for the attention of a famous female physicist.

When Leonard and Penny aren’t speaking, Sheldon goes to extremes to keep them both happy.

A fight between Leonard and Penny threatens their relationship, while Sheldon battles Wil Wheaton in bowling.

Sheldon’s friends come to his aid when his fear of public speaking stands between him and a coveted award.

When the guys find a ring from “The Lord of the Rings” at a garage sale, it threatens to tear them apart.

Sheldon winds up in traffic court when he gets a ticket because of Penny.

Leonard can only bring one guest on a trip to see CERN’s Large Hadron Collider (the world’s largest and highest energy particle accelerator) in Switzerland on Valentine’s Day.

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

A robbery of their apartment sees Leonard and Sheldon call on their friends to devise a security system.

Leonard is aghast to find out a secret of Penny’s: she believes in psychics. Meanwhile, Sheldon tries to assist Koothrappali in picking up a girl at a university party.

Leonard’s mother (Christine Baranski) visits, which pleases Sheldon but upsets Leonard. .

Sheldon attempts to help Penny understand Leonard’s work, and Wolowitz becomes jealous when Leonard starts hanging out with his new girlfriend.

Barry Kripke embarrasses Sheldon on NPR, and the gang rallies to help him get his revenge. Wolowitz, desperate to keep his romance with Bernadette alive, gets advice from a fantasy version of Katee Sackhoff.

With Leonard, Howard and Raj away camping in the desert, an injured Penny has only Sheldon to rely on.

A squabble between Leonard and Penny sees Sheldon playing mediator, though out of his own incovenience from the situation rather than altruism.

Sheldon teaches Leonard how to understand football while a kite-fighting incident threatens Howard and Raj’s friendship

Sheldon seeks revenge on his nemesis, Wil Wheaton; Wolowitz wants Penny to set him up with one of her friends.

Raj must find a new job or be sent back to India, but Sheldon has a solution, which leaves Leonard and Penny dealing with Howard as third wheel.