Leonard is disappointed when Penny develops an interest in an attractive physicist at the university. Meanwhile, Sheldon struggles to find an appropriate Christmas gift for Penny.
Howard becomes depressed after Penny makes a cruel statement about his love life, while the rest of the guys prepare for a grudge killer robot duel against an obnoxious colleague at the university.
Leonard becomes concerned when his date with Penny ends abruptly and she starts blowing him off. When told the truth, Sheldon would rather move out than keep Penny's reasons a secret from Leonard.