When Penny finds out Alex has a crush on Leonard, Sheldon gets himself and the rest of the guys in trouble with Human Resources whilst trying to solve the problem.
The guys are stranded in the middle of nowhere when Leonard's car is stolen on the way to the Bakersfield Comic-Con. Back home, the girls try to figure out why the guys are so fascinated with comic books.
Sheldon is forced to work with Kripke on a project and must concoct an elaborate lie when he can't hold up his end of the work. Howard and Raj get superhero figurines made of themselves.
Leonard moves in with Penny after a fight with Sheldon, which causes Amy to want to move in with Sheldon. Meanwhile, Raj has a frightening experience with Howard's mother.
Sheldon gets Alex to buy a Valentine's Day gift for Amy. Leonard, Penny, Howard and Bernadette have a disastrous dinner together. Raj and Stuart host a "Lonely People" party at the comic book store.
Raj falls apart after his date sneaks out on him, and Sheldon reluctantly returns the favor after Penny helps him out with his "Fun With Flags" program.
Leonard, Sheldon and Howard give lectures on science to junior high students. The girls ditch work to go to Disneyland. Raj devises a date for Lucy that fixes their social anxiety problems.
A date between Raj and Lucy takes both of them out of their comfort zones. After a trip to Las Vegas goes awry, the girls join in on a Dungeons and Dragons game, which causes Amy and Sheldon to re-evaluate their relationship.
Penny is thrown for a loop when Leonard is offered a job overseas, but the news is an even bigger shock to Sheldon. Raj and Lucy's relationship comes to a crossroad.
Sheldon and Penny bond over missing Leonard. Howard tries to help Raj get over his breakup with Lucy. Amy and Bernadette take a trip together to a biology convention.
Sheldon feels betrayed when Leonard returns from the North Sea and wants to spend his time with Penny instead of him. Howard's latest foray into helping his mother has some disastrous side effects.
Sheldon gets mad at Amy for ruining one of his favorite movies, Raj and Stuart try to make their online dating profiles more appealing, and Leonard tries to play the sympathy card with Penny.
Howard plans something special to celebrate the anniversary of his first date with Bernadette. Sheldon is conflicted when he makes a major scientific breakthrough but some details have to be corrected.
Sheldon seeks payback when Arthur "Professor Proton" Jeffries asks Leonard for help on a project instead of him. Raj gets upset at Howard for crashing his night with the girls.
The gang spend Thanksgiving at Mrs. Wolowitz's house. Howard tries to bond with his father-in-law, and a mistake from Penny's past comes back to haunt her.