Island of Promise — Diana Sheridan

Jim has been lonely since the sudden breakup of his last relationship, and his blah life as a bookkeeper is boring...but when he hits the lottery, his whole life changes. With his newfound wealth, he books a vacation at a deluxe resort on a private tropical island. Aboard the resort's yacht, he meets Anton, a dark-haired European minor nobleman, and falls for him. Not content with the many activities the resort offers, Anton proposes a daring adventure that's strictly against the rules. After the two lovers get lost in the wilds of the jungle and Jim suffers an injury, they stumble upon a secret-and some bad guys. Now that the couple knows too much, the bad guys want to do away with them. Imprisoned, Jim and Anton search for a means of escape before the criminals put an end to them.