Professor Proton helps Sheldon deal with grief; Leonard gets into a competition with Penny; Bernadette and Amy prepare a "Star Wars Day" gift for the guys.
Episode: 22
The Proton Resurgence
Leonard and Sheldon hire the host of their favorite childhood TV show to perform for them; Bernadette and Howard run into trouble while dog-sitting for Raj's pet.
The Stag Convergence
After the guys throw Howard a bachelor party, Bernadette reconsiders marrying him after learning about his sexual history.
The Wildebeest Implementation
Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.
The Staircase Implementation
Leonard tells Penny about how he met Sheldon for the first time…and what happened to the elevator.
The Classified Materials Turbulence
Penny's second date with Stuart sees her making a comment that gives Leonard new hope for a relationship with her. Wolowitz realizes there's a crucial error in a NASA project he's working on.
Guidance
Thanks to Misa, the Task Force now knows the identity of the new Kira and L plans an elaborate scheme to smoke him out of hiding.