After tampering with Sheldon's Arctic-expedition data, the guys follow him back to Texas, which threatens Leonard's chances for romance with Penny.

In the second-season finale, Leonard gets ready for a three-month long science trip, and he and Penny come to terms with their feelings for each other. ~ Bill Ecklund, All Movie Guide

While on a date with Stuart, Penny makes an unexpected discovery regarding Leonard; and Wolowitz asks for his friends' help on his NASA project when he uncovers a design flaw. ~ Bill... Full summary

Leonard, Koothrappali and Wolowitz go to Las Vegas, and Sheldon is locked out of the apartment, leaving him no choice but to stay with Penny. ~ Bill Ecklund, All Movie Guide

Penny is romanced by a friend of the guys' while at a comic-book store. Meanwhile, Leonard and Wolowitz search for love at a bar's ladies' night. ~ Bill Ecklund, All Movie Guide

Penny develops a rivalry with a pretty woman who moves into the building. ~ Bill Ecklund, All Movie Guide

Penny starts a hair-product business that suffers when her friends, particularly Sheldon, become involved. ~ Bill Ecklund, All Movie Guide

The guys' trip to San Francisco takes a detour once they learn that actress Summer Glau (appearing as herself) is on their train. Astrophysicist George Smoot also has a cameo. ~ Bill... Full summary

A paintball game has Penny and Sheldon engaging in their own personal battle and Leslie and Wolowitz finding romance. ~ Bill Ecklund, All Movie Guide

Leonard suffers through a dreadful visit from his mother (Christine Baranski) that ends up bringing him and Penny closer. ~ Bill Ecklund, All Movie Guide