Master of Judo

From publisher blurb: You are a black belt in judo and have been offered the summer job of a lifetime teaching this martial art to the steppson of a billionaire. Better still, you'll do your teaching on a yacht headed for exotic ports in the Caribbean Sea. But when your student is mysteriously kidnapped during one of your island visits, it's up to you to find him. Do you dare trust your suspicious shipmates to assist you? Or should you rely on your judo mastery and the local police to help you with the hunt?