William Monk is a mid-Victorian Londoner who wakens in a hospital bed, with no memory and no knowledge of who he is. He learns bit by bit that he is a brilliant, feared and disliked detective in the police. He has to solve a complex case at the same time learning who are his friends, who his enemies, and worst of all, what was his own involvement in the case. Throughout this and later cases, he is assisted by Hester Latterly, a remarkably brave nurse who served during the Crimean War with Florence Nightingale.