The Big Bang Theory - Season 4, Episode 6: The Irish Pub Formulation

Raj's (Kunal Nayyar) hot sister drops by for a visit and he asks that Howard (Simon Helberg) stay away from her. Sheldon (Jim Parsons) finds out that Leonard (Johnny Galecki) has a secret affair and is forced to keep it to himself. Individual trust is put into question when Leonard confesses to a betrayal.

Channel: CBS
Air Date: 28 October 2010