Tim Conway and Don Knotts play two bumbling Scotland Yard investigators out to solve a double murder in this silly send-up of vintage, "old dark house" films. The intrepid Winship (Knotts) and his assistant Tart (Conway) arrive at a Gothic mansion occupied by the grieving heiress Phyllis (Tricia Noble), whose parents have just perished under suspicious circumstances. Meanwhile, a quirky crew of servants ranging from a butler with serious rage issues to a samurai warrior cook and busty maid with a bubbly personality all display likely motives for murder. As a mysterious, black-cloaked killer methodically dispatches with the help, the inept investigators search for clues while being watched by paintings with moving eyes, exploring a frightful a torture chamber, and attempting to communicate with their superiors at Scotland Yard via carrier pigeons who never seem to reach their intended destination.