A German crime thriller from the year 1963 and one of the Edgar Wallace Films.One night at Blackmoor Castle, a masked man appears before its owner Lucius Clark and demands that he hands over a batch of diamonds he stole some time ago. Clark refuses, and as he tries to sell the diamonds, the masked man hinders the process by killing people around the castle.
Examples in this film:
- Antagonist Title: Combined with The X of Y to keep the antagonist's identity hidden.
- Ax-Crazy: Anthony, who is ready to kill to get the diamonds.
- Calling Card: The Strangler leaves the letter M on his victims' foreheads.
- Evil-Detecting Dog: Castle's dogs start barking whenever the Strangler is nearby.
- Evil Uncle: Defied. When Anthony suggests to Lucius that "an accident" should befall on his niece so they'd get her money, he is enraged and socks Anthony to the jaw.
- MacGuffin: The stolen diamonds.
- Off with His Head!: The corpse of castle's gardener is found without his head.
- Playing Possum: The Strangler lies on the ground pretending to be hurt to get the Clark's gardener (who was sent to take the stolen diamonds to his partner) to come closer.
- Red Right Hand: One of Lucius's fingers is missing and the Strangler seems to share this trait.
- Secret Path: A robber owned the Blackmoor Castle long time ago, and he made sure that it has lot of secret tunnels within it.