4. The Staircase Implementation
Season 3, Episode 22
Title Reference: Leonard's rocket fuel breaks the elevator so everyone has to use the stairs. After having a fight over the thermostat temperature Leonard goes to Penny's apartment where he tells the story of how he and Sheldon ending up living together. After responding to an ad for a roommate, Leonard visits the apartment, along the way he meets Sheldon's former roommate (Walking Dead's Steven Yeun) who warns him to run. The episode shows the origin of Sheldon and Leonard's living arrangement and friendship, and their subsequent friendship of Raj and Howard and the implementation of the Roommate Agreement. Leonard, Raj and Howard start off not liking Sheldon and trying to avoid him but change their minds when he saves Leonard by sealing unstable rocket fuel that Leonard had made in the elevator. This explains the elevators prolonged disuse.
Best Moment: Sheldon saves Leonard from certain death and simultaneously breaks the elevator by putting the unstable rocket fuel in the elevator and closing the doors.