The great James W Hall! Haven't read one of his in AGES and this is one I've read before, but I always liked the the story, a clever but unstable young man targets a cruise ship for sabotage and sheningans. Thorn gets dragged in when his friend Sugerman gets injurred, there's also a (beautiful of course, ah, the 80s trope of even less chauvanistic writers to dwell lovingly on the beauty of their female characters even when, as in this case the beauty is a curse, getting close to the idea that it's not her or anyone's looks it's bloody men) runaway heiress, tricked on board by the unstable guy who has an unhealthy fixation on her. Remember Speed 2, the one set on a boat? Pity they didn't give Hall a truck full of cash for the rights to this and used the plot, easily ooomphed up for cinema with some explosions and shootouts. Ah well.