Penny realizes that Leonard never celebrated his birthday, and when she tried to throw him a surprise party, she failed, so she teams up with Sheldon, Howard, and Raj to help throw a surprise party for Leonard.
Penny, Amy, Bernadette, Emily, and Alex are hanging out but then they decide to plan a birthday party for Leonard. Penny texts Sheldon, Raj, Howard, and Stuart to come over in order to help plan Leonard's surprise party. The next day Penny is working with Sheldon, Raj, Howard, and Stuart in setting up the comic book store for Leonard's party. Alex, Emily, and Amy are baby sitting Steve and Debbie. Bernadette is distracting Leonard with experimental physics. Later, Alex, Emily, and Amy bring Steve and Debbie with them to the comic book store. Bernadette tells Leonard she has an errand, as excuse to change and go to Stuart Comics to surprise Leonard. Leonard then finishes up, and gets a text from Sheldon to come to the comic book store. When Leonard arrives, everyone surprises him and has a good party.