The Big Bang Theory Season 6 Episode 17 The Monster Isolation

Sheldon's fear of monsters becomes an issue when he gets locked out of his apartment and must spend the night at Penny's. Meanwhile, Leonard has to adjust to a new way of doing things when Sheldon starts using a new virtual assistant AI system that is more efficient than his own. Howard and Raj attempt to solve the mystery of a strange letter that was sent to their office, and Bernadette struggles to deal with her guilt over not being able to spend more time with her father before his passing. As the night wears on, tensions rise and secrets are revealed, leading to an emotional and unexpected conclusion.