Finger weg von meiner Schwester

Sheldon, Leonard and Howard are in the canteen eating lunch, and Howard is complaining about the food. Then comes Raj with his younger sister Priya, who is visiting her brother during a business trip to Los Angeles. When she asks for the way to the toilet, Leonard offers to show her the way. Raj uses the absence of his sister to warn the remaining guys not to fool around with Priya. However this is especially addressed to Howard. The latter is outraged, as he finally is in a happy relationship with Bernadette. Besides, he has concluded a pact with Leonard, that neither of them would ever make a pass on Priya for the sake of their friendship. But meanwhile, Leonard and Priya start making out in front of the toilet.

Howard asks Raj what he has planned for the day with Priya. However, Raj has not yet thought about this, so Sheldon proposes that they undertake a tour of the city. But he garners only little enthusiasm from the others.

When Leonard and Priya intentionally return separately from the bathroom and encounter the boys, they behave as if nothing had happened.

Sheldon is deep in the middle of an old computer game and plays it until late in the night. Much to Leonard's displeasure, because he expects Priya. Because Sheldon does not go voluntarily, Leonard has to resort to a trick to get him to sleep. Finally Leonard manages to smuggle Priya into his room. The next morning, Priya oversleeps. She must be back at Raj's place early in the morning, to avoid arousing suspicion. Leonard is sad that Priya is going away again and asks her if he can go with her to India. But Priya rebuffs him, as she only wants to have an affair with him. Since Sheldon is already awake, it is not easy for Priya to get out of the apartment unseen. At the door, both are caught by Sheldon.

On the way to the University, Sheldon gives Leonard a guilty conscience, because of the pact he and Howard swore. Leonard begs him to keep silent. Sheldon then works out an alibi, since he can only lie badly. With a fake phone number and lock of hair, he has invented another woman for Leonard to date. But when the conversation at lunch comes to the subject, Leonard cannot lie to Raj and finally tells him the truth. Raj is furious and can only be pacified when he learns that Priya has rebuffed Leonard. Raj goes back to sitting opposite Leonard and that triggers a series of confessions about who has done what to whom at which time. Ultimately all four apologize to each other.