The Big Bang Theory: Season 4, Episode 6

4 - 6: The Irish Pub Formulation

Raj's sister Priya (Aarti Mann) visits and inadvertently causes trouble for the friends. She and Leonard apparently have a history, despite Leonard's pinky swear with Howard that they would not interact with her in deference to Raj. They hook up, but are discovered by Sheldon, who tries to devise an elaborate, flawless lie to cover it up. Leonard cannot persist in the deception and reveals the assignation. The guys then confess to all of the deceptions they have perpetrated on each other: Howard dropped Raj'siPhone