Season synopsis
Contains spoilers for this season and earlier seasons.
Leonard Hofstadter and Sheldon Cooper are Pasadena physicists and roommates whose routines change when aspiring actor and Cheesecake Factory waitress Penny moves across the hall. Leonard immediately imagines a romance; Sheldon doubts the odds. Their attempt to help Penny retrieve a television from her ex-boyfriend Kurt ends with Leonard and Sheldon returning without their pants, while Penny responds with kindness and invites them to dinner. Howard Wolowitz and Raj Koothrappali, their engineer and astrophysicist friends, are already part of the group that shares meals, games and trips to work.
Leonard's crush does not become a simple courtship. After he sees Penny kiss a man she has been casually seeing, he asks university physicist Leslie Winkle out; their experimental kiss does not lead to a relationship. Sheldon then encourages Leonard to ask Penny, but Leonard avoids admitting that he means a date. The season also tests the friends' loyalty: when Sheldon is fired and retreats into bizarre projects, Leonard calls Sheldon's mother Mary. Her visit gets Sheldon back to the university and his ordinary life.
Penny's place in the group grows through practical kindness as well as flirtation. She arranges a surprise birthday for Leonard after learning he has never celebrated one, and helps Sheldon through social situations even when his rules frustrate her. In the finale, Penny breaks up with Mike after he posts private details about their relationship online. Leonard comforts her, gives poor advice that briefly sends her back toward Mike, then asks her on a date. She accepts, so his long-running hope becomes a first date, not an established relationship.