Episode 1 | The Electric Can Opener Fluctuation

After returning from the North Pole, a conflict among the guys sends Sheldon back to Texas and interferes with Leonard's reunion with Penny.

Episode 2 | The Jiminy Conjecture

Leonard and Penny's first night together goes awkwardly. Sheldon and Howard wager on the species of a cricket.

Episode 3 | The Gothowitz Deviation

Sheldon attempts to covertly alter Penny's habits, while Howard and Raj try their luck meeting women at a Goth-style club.

Episode 4 | The Pirate Solution

When Raj has to find a new job or be sent back to India, Sheldon's solution leaves Leonard and Penny dealing with Howard as the third wheel.

Episode 5 | The Creepy Candy Coating Corollary

Leonard is forced to ask Penny to set Howard up with one of her friends, while Sheldon seeks payback against sci-fi star Wil Wheaton.

Episode 6 | The Cornhusker Vortex

Leonard tries to learn about football to fit in with Penny's friends. Meanwhile, a loss in a kite war threatens to end Raj and Howard's friendship.

Episode 7 | The Guitarist Amplification

Sheldon is caught in the middle when Leonard and Penny argue about Penny's friend staying at her apartment.

Episode 8 | The Adhesive Duck Deficiency

Penny is forced to turn to Sheldon for help when she dislocates her shoulder in the bathtub. Meanwhile, the rest of the guys accidentally get stoned in the desert while waiting for a meteor shower.

Episode 9 | The Vengeance Formulation

Sheldon plans revenge after Kripke humiliates him on the radio. Howard develops doubts about his relationship with Bernadette.

Episode 10 | The Gorilla Experiment

Sheldon attempts to help Penny understand physics to impress Leonard, while Howard becomes jealous when Bernadette takes an interest in Leonard's research.

Episode 11 | The Maternal Congruence

Leonard's mother makes a visit to his dismay and Sheldon's delight.

Episode 12 | The Psychic Vortex

Raj talks Sheldon into being his wingman at a university mixer. Leonard has trouble dealing with Penny consulting a psychic.

Episode 13 | The Bozeman Reaction

When their apartment is robbed, Leonard and Sheldon turn to Howard and Raj to create a state-of-the-art security system.

Episode 14 | The Einstein Approximation

Sheldon wreaks havoc when he is stumped by a difficult physics question.

Episode 15 | The Large Hadron Collision

When Leonard is offered a trip to Switzerland on Valentine's Day to visit the CERN laboratory, Sheldon uses any and all means to be his guest instead of Penny.

Episode 16 | The Excelsior Acquisition

Sheldon misses an opportunity to get Stan Lee's autograph because he has to make an appearance in traffic court.

Episode 17 | The Precious Fragmentation

The guys' friendship is threatened when they find a ring from the "Lord of the Rings" trilogy.

Episode 18 | The Pants Alternative

Sheldon seeks help from the rest of the gang in overcoming his fear of public speaking when he receives an award.

Episode 19 | The Wheaton Recurrence

Sheldon takes on Wil Wheaton in a game of bowling. Leonard and Penny's relationship comes to a crossroad.

Episode 20 | The Spaghetti Catalyst

Sheldon is forced to go behind Leonard's back to spend time with Penny following their breakup.

Episode 21 | The Plimpton Stimulation

Chaos ensues when a nymphomaniac physicist visiting Sheldon hooks up with Leonard.

Episode 22 | The Staircase Implementation

Leonard tells Penny about how he and Sheldon became roommates and what happened to the elevator.

Episode 23 | The Lunar Excitation

Penny has a night of angry, drunken sex with Leonard, much to his confusion. Meanwhile, Howard and Raj search for Sheldon's perfect match online.