Bernadette and Wolowitz leave their kids for the first time; Penny and Leonard try to keep a secret; Sheldon and Amy stick together; and Koothrappali makes a new friend, as the gang travels together into an uncharted future.
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.
When Amy's parents and Sheldon's family arrive, everybody is focused to make sure all wedding arrangements go according to plan - everyone except the bride and groom.
Penny is forced to turn to Sheldon for help when she dislocates her shoulder in the bathtub. Meanwhile, the rest of the guys accidentally get stoned in the desert while waiting for a meteor shower.
The gang spend Thanksgiving at Mrs. Wolowitz's house. Howard tries to bond with his father-in-law, and a mistake from Penny's past comes back to haunt her.
