When Leonard meets David Underhill, an award-winning scientist who is the exact opposite of Leonard (handsome, cool and intelligent), Leonard is put in the worst situation he can imagine when David and Penny become more than friends. Meanwhile, Penny buys a Christmas gift for Sheldon, but unfortunately, Sheldon thinks of Christmas as an annoying part of the year where the recipient of a gift is tied to a promise to give the sender a gift back, and Sheldon doesn’t know what to do.