When his mother comes for another visit, Sheldon is disappointed that she's stopped being the mother he wants her to be.
Sheldon irks the gang over his obsession with proper Christmas gift protocol. Leonard is crushed when Penny dates a colleague of his.
With Sheldon rattled and impossible to be around after meeting Dennis, a 15-year-old physicist who's smarter than he, the rest of the guys search for a way to eliminate the threat.
Leonard and Sheldon each lie to avoid hearing Penny sing in a production of Rent. However, Sheldon's lie becomes a bit too complicated for its own good.
Raj's parents set him up on a blind date, and when he discovers he can talk to her, she shows interest in Sheldon.
Sheldon's getting fired forces him to explore what life has to offer outside physics, leaving Leonard to take drastic action to snap his friend out of his funk.