The Monk once worked as an advisor to Yartek. (PROSE: No Future) Yartek discovered how to resist the Conscience of Marinus. Invading the building where the Conscience was kept, Yartek and his followers killed Arbitan. Yartek then posed as Arbitan — dressing in the Keeper's robe, keeping in the shadows and hiding his features beneath the hood of the garment — to get the keys to the Conscience from Ian Chesterton. He was killed in the destruction of the Conscience when he placed a false key in the machine resulting in an explosion. (TV: The Keys of Marinus)