Agnes is a non-canonical character who was created for the ITV's 2010 adaptation of The Secret of Chimneys. She was a parlour maid working at Chimneys long before before the main events in the episode. In the opening scene, she is shown being killed during a house party at Chimneys in 1932. However when her case was discussed some 23 years later during the events in the episode, most people thought she had disappeared without trace just after the party and that she had stolen the Mysore diamond which belonged to Lady Somerset.
Agnes is portrayed by Laura O'Toole.