The Mysterious Caravan — Franklin W. Dixon

When the Hardy Boys take a winter vacation in Jamaica, Joe finds an ancient bronze death mask washed up near their beach house during a violent storm. Helping the Hardys and their friends in this bizarre mystery is William, a Jamaican boy, who flies to New York with startling news, only to be intercepted and held for ransom -- the death mask! Frank and Joe must rescue William, plunge into their father's airline-ticket theft case, and fly into a maze of danger in Africa.