The Mysterious Caravan – Franklyn 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.