The Caribbean Cruise Caper (The Hardy Boys #154) Reissue edition

All Aboard for a Major Mystery
Frank and Joe have the ultimate case on their hands: to judge the sleuthing skills of five teen dtectives in a contest sponsored by Teenway magazine. Even more cool -- the contest takes place on a caribbean cruise ship! But it's not long before suspicious pranks threaten to ruin the contest: one of the Teenway interns nearly falls overboard, the "mystery scene" the contestants studied gets tampered with, and someone may have poisened the food!
How can the Hardys solve this titanic mystery? With the help of five teen detectives, of course -- along with their own expert investigating skills. But they's better move fast, because a culprit lurks beneath the caribbean sun -- and it's sink or swim for Frank and Joe.