The Big Bang Theory spoilers

The episode is titled "The Bad Fish Paradigm". The plot line is after Leonard and Penny go on their date (they don't show the actual date), Wolowitz and Raj start analyzing his date by viewing video footage they secretely taped from the hallway, leaving Leonard feeling nervous. Later Penny confides in Sheldon her concerns about having a relationship with Leonard. Sheldon feels that he has been tricked into keeping a secret and admits to Penny that he is not good at keeping secrets. To avoid telling Leonard the secret, Sheldon moves out of the apartment and briefly stays with Raj and then Wolowitz. Wolowitz becomes so frustrated with Sheldon that he drugs him with Valium and returns him to Leonard. While he is drugged, Sheldon tells Penny's secret to Leonard. Leonard attempts to fix the situation with Penny but only further complicates the issue.