A group of guests gather for a weekend party at the remote and eerie Black Dudley estate. During a strange ritual involving an ancient dagger, their host, Colonel Coombe, dies under suspicious circumstances. As the guests are held in the house by dangerous criminal figures, tensions rise and secrets surface. Amid the chaos, the clever and unflappable Albert Campion-appearing here for the first time-helps unravel the mystery behind the murder, the dagger, and the criminals controlling the house.