When Wolowitz dresses up as Sheldon for Halloween, Sheldon seeks retaliation at Leonard and Penny's Halloween party. Also, Leonard is shocked that Penny doesn't remember their first kiss.

Cast: Kaley Cuoco, Pamela Adlon, Mayim Bialik, Johnny Galecki, Rati Gupta, Simon Helberg, Kunal Nayyar, Jim Parsons, Brian Posehn, Melissa Rauch, Kevin Sussman, Stephen John Williams