A ghost debunker is touring Europe with his niece when he gets a new case to tackle.

Professor Tidewater tours Ireland with his two daughters to investigate the origins of ghost stories. After the girls leave him at Belmore Castle, reputed to be haunted, the Hindu caretaker Sakes relates the following tale: Henry Claven, Sakes' master, courted his beautiful neighbor Betty Truesdale, but when she became engaged to Captain Bob Lambert, Claven precipitated a duel by telling Lambert that he knew his mother was a negress