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.
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.
After the guys throw Howard a bachelor party, Bernadette reconsiders marrying him after learning about his sexual history.
Raj attempts to cure his social anxiety disorder while Penny uses Bernadette to spy on Leonard and his girlfriend.
Leonard tells Penny about how he met Sheldon for the first time…and what happened to the elevator.
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.
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.