Tom Stone has never been fond of going abroad. Now that he’s no longer on the police force, though, his partner Mary has a suggestion for a post-retirement holiday: a river cruise along the Mekong.In theory, the trip is an opportunity to relax and take in the scenery of Vietnam. It’s also a chance to meet people who lived through the Vietnam War, on both sides, and learn more about the country’s scarred history. But, when one of the passengers disappears under suspicious circumstances, it turns out that it might not be so easy to leave detective work behind.