Masquerade (1) - S1.E6

Mannering is invited by Sir Frederick Alton to his country home. When he enters the house he hears a woman crying for help. As he goes to help he's knocked unconscious. He wakes up to discover that he has a twin double. Mannering manages to change places with the double and his captors kill the man they belive to be the Baron. They then let him in on their plans to steal the Crown Jewels only for Cordelia to turn up at the wrong moment.