Leonard and Sheldon's friendship is put to the test when Leonard wants to present a paper they co-authored at a physics convention, but Sheldon doesn't.
Leonard lies to Penny so he and Sheldon can get out of watching her perform, but Sheldon believes that the lie has too many loose ends, so he comes up with a new, unnecessarily complex one to replace it.
Sheldon decides to give up his work and focus on other tasks when a 15-year-old prodigy joins the university, so the other guys come up with a plan to get rid of him.
Sheldon becomes so intent on demonstrating his intellectual superiority over the other guys that they kick him off the Physics Bowl team and replace him with his nemesis, Leslie.
Penny gets mad at the guys when their full scale model of a time machine causes her to miss work, which prompts Leonard to give up all of his nerd memorabilia.
Leonard becomes concerned when his date with Penny ends abruptly and she starts blowing him off. When told the truth, Sheldon would rather move out than keep Penny's reasons a secret from Leonard.
Penny plans revenge when Sheldon bans her from his and Leonard's apartment, while Howard and Raj use the latest technology to try to find the house being used in "America's Next Top Model."
Leonard tries to slow down his relationship with Stephanie when he realizes that they are living together, while Sheldon becomes convinced that he has an untraceable disease.
Leonard is disappointed when Penny develops an interest in an attractive physicist at the university. Meanwhile, Sheldon struggles to find an appropriate Christmas gift for Penny.