In the Season 6 finale, Penny is thrown for a loop when Leonard is offered a job overseas, but the news is an even bigger shock to Sheldon. Raj wants more out of his relationship with Lucy than she can handle.
After Leonard and Sheldon get in a fight over the thermostat, Leonard goes to Penny's apartment and tells her about how he met Sheldon for the first time and how they became roommates...and what happened to the elevator.
Penny has a night of angry, drunken sex with Leonard, which Leonard soon misinterprets as something other than a mistake. Meanwhile, Wolowitz and Koothrappali search for Sheldon's perfect match online.