With Bernadette, Howard and Raj going to the movies, Penny going to work and Sheldon getting a ride from one of those groups to the train store, Leonard finds himself alone in the apartment with Amy. At first, Leonard is ill at ease with Amy being there, but soon, he grows comfortable with her presence and her contendedness to just sit. Sheldon returns from the train store to find Amy still in the apartment. She tells him that she's rescinding her invitation to accompany her to a wedding that weekend and instead, Leonard is going to be her date. Meanwhile, Bernadette gets a surprise when Howard talks about how the two of them are going to move in with his mother once they're married. They get into a fight but he soon convinces her to just spend the weekend with them to try it out. Bernadette agrees and soon Howard discovers that he might be marrying a too-close-for-comfort version of his mother. At the wedding, Amy takes Leonard to task for always being a sad sack. She convinces him to dance with her and he finally agrees. They have a great time and Leonard gets so enthusiastic that he tries to do the splits, thus straining his groin. It doesn't damper his good time and at the end of the night, Leonard thanks Amy and kisses her on the cheek. Amy immediately goes to Penny and tells that she unwittingly made Leonard fall in love with her. When Leonard tells Sheldon that he and Amy had a good time and she's a lot of fun, Sheldon immediately karate chops Leonard in the neck, exclaiming, "She's not for you!" Sheldon gets territorial. About a girl.