The Cuban Affair by Nelson DeMille

Daniel McCormack, army vet, is living the good life as a tour boat captain in Key West when he's approached by a man named Carlos and a beautiful woman named Sara. They want his help to get to Cuba to retrieve a fortune that had been secreted by a Cuban banker for his customers before they had to flee when Castro took over. Mac is promised $3 million for his efforts. Though his gut is telling him this is a bad idea,  the thought of financial security--and spending time with the lovely Sara--persuade him to take a chance. Of course, the plan is nebulous at best. The people he's working with are not telling him the whole truth. And there are factors beyond his control at work in Cuba itself--like a randy tour guide who has eyes on Sara.

It's a good story with lots of twists and turns. And you learn a fair bit about modern-day Cuba. So it would be a good book for a rainy weekend or a long flight.