The Hardy Boys #55: The Witchmaster's Key book by Franklin W. Dixon

There is not time for explanations when Mr. hardy telephones Frank and Joe form 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. When the Hardys learn about the strange disappearance of Lord Craighead, the plot deepens. Danger follows them to Ireland as Frank and Joe survive a shipwreck and find a clue from a frightened white which that leads to the torture chamber of a black witches’ coven, all in search of the telltale Witchmaster’s Key.