An appalling triple murder in Edwardian Manchester leads to a trial which is simplicity itself. The evidence is unchallenged, the confession sound. But before the hangman can do his work, an appeal is lodged. The guilty man was supposedly insane when he killed Edward, Eliza and Lucia Tallboys.

With public outrage filling the papers, Dr Alice Urquhart of High Helmsley Asylum must investigate the true nature of the murderer's condition as quickly as possible. And determine at the same time why one of her other patients is convinced that Mr Dry, the so-called Deptford Assassin, is coming to kill him...