Penny wishes Leonard a happy birthday which she knows is this upcoming Saturday, when she expects him to at least come in for his free piece of birthday cake at the restaurant. She is shocked to learn that Leonard not only does not celebrate his birthday, but that he's never had a birthday party. Regardless of Leonard's wants, Penny decides to throw him a surprise party. Although she gets help from Sheldon, Howard and Raj, the preparation for the party does not go to her plans, including needing to help Sheldon buy a gift, Howard not being able to get Leonard out of the apartment, and Raj not being able to decorate the apartment since Leonard's there. Will Leonard enjoy his first birthday party after all this difficult effort?