There is no time for explanations when Mr. Hardy telephones Frank and Joe from the West Coast and sends them flying off to England to help his old friend Professor Rowbotham. Their stay in East Anglia begins with a weird omen, as they witness the bizarre funeral of an old witchmaster. From then on, strange things happen. They are shadowed, trapped, sprung upon by a huge black dog, and smitten by an old crone's curse. Who are their enemies? The same people who burglarized the professor's witch museum and robbed him of his life's investment? When the Hardys learn about the strange disappearance of Lord Craighead, the plot deepens. Danger lurks everywhere and follows them to Ireland and the Isle of Man. After surviving a shipwreck in the storm-tossed Irish Sea, the clue of a frightened white witch leads them into the torture chamber of a black witches' coven. Frank and Joe barely escape alive in the final struggle with their fanatic adversaries, from whom they finally snatch the telltale Witchmaster's Key! - Flyleaf.