Scotland Yard must discover why people are being murdered by a monstrous dog at Blackwood Castle.

The sister of a famous, but as yet uncaught, criminal named The Hexer is murdered. Inspector Higgins of Scotland Yard believes that The Hexer will surface to take his revenge on his sister’s killers, and plans to set a trap to finally capture him. However, soon bodies start piling up, and it looks as if The Hexer may get away yet again.