In the early 20th century, a tense mystery unfolds at a secluded English country mansion where the murders of Lord Randolph Morley and Lady Victoria Morley appear to have been carried out by a cloaked figure in a black cape. The crime scene sets the stage for a clash between two American detectives, Inspector Winship Don Knotts and Dr. Tart Tim Conway, who have been reassigned to Scotland Yard after troubles back home. They arrive with a letter from the late Lord Morley himself, a plea for them to take up the case and uncover the truth behind his supposed demise, hoping this unusual petition will expose the real killer lurking in the manor’s corridors.
They soon encounter the Morleys’ world—an opulent but suspicious estate filled with people who may know more than they admit. At the center of the intrigue is the Morleys’ heiress and adoptive daughter, Mistress Phyllis Morley Trisha Noble, a striking figure whose presence adds a volatile mix of charm and danger to the investigation. The staff, each more peculiar than the last, move through the halls like living ciphers: a samurai, a hunchback, a busty maid, a gypsy, and an insane butler, all seemingly loyal to a family history steeped in wealth and secrecy. As the two detectives poke around, these staff members are seemingly killed one by one, only for their bodies to vanish before anyone can present them to the heiress and prove the murders truly happened.
Frustration grows as the duo tries to maintain contact with Scotland Yard via homing pigeon signals, but the birds keep dying before a message can be sent, turning the investigation into a comic, almost farcical chase against time and superstition. The vast network of hidden passages beneath the mansion becomes a labyrinth of danger, leading Winship and Tart into a so‑called torture chamber where Winship is ensnared in a deadly trap. Just when all seems lost, the cape-wearing figure—the elusive The Shadow—surfaces and expertly rescues Winship from the peril, adding a supernatural edge to the already tangled mystery.
A dangerous twist follows as a boa constrictor slithers into the scene, driving the detectives into a trash compactor where they narrowly survive being compressed into a bale of garbage. Emerging into the light, they confront a startling development: the heiress is preparing to flee with Morley’s fortune. She confesses to killing the Morleys in a bid to feed a gambling habit, intending to vanish with the money and start anew. But as she recoils in fear and steps backward into a flower bed, the shadowy figure who has been hiding in the dirt grabs her, prompting a fainting spell. The caped killer drops the dramatic reveal and removes the cape, exposing himself as Lord Morley, who had staged the whole affair to uncover his wife’s lover and to force the truth into the open.
Morley explains the elaborate ruse: he was “dead” and in hiding, having written the letter to Scotland Yard to draw Winship and Tart into a carefully planned investigation. The other staff members then appear, having faked their own deaths as part of Morley’s overarching scheme to root out the truth behind the murders and the heiress’s gambling debts. With the confession on the table, the heiress is arrested, and Winship and Tart are rewarded with a rare sarcophagus that is placed in their car as a token of the affair’s resolution.
As the detectives depart, they debate a lingering, almost mythical threat—the existence of wookalars, fearsome, manlike creatures said to possess superhuman strength and pig‑like faces. The car’s tires screech as they speed away, and their argument remains unresolved until a final, chilling sight: a wookalar bursts forth from the sarcophagus, causing their car to careen down the road in terror, leaving the audience with a last, wild twist to close the mystery.
