«Drowned Hopes» by Donald Westlake

An old cellmate asks Dortmunder for help robbing a reservoir In his day, Tom was a hard man. He came up with Dillinger in the 1930s, and pulled a lot of high-profile jobs before the state put him away. They meant it to be for good, but after twenty-three years the prisons are too crowded for seventy-year-old bank robbers, and so they let the old man go. Finally free, he heads straight for John Dortmunder’s house. Long ago, Tom buried $700,000, and now he needs help digging it up. While he was inside, the government dammed a nearby river, creating a reservoir and putting fifty feet of water on top of his money. He wants to blow the dam, drown the villagers, and move to Acapulco. If Dortmunder wants a clean conscience to go along with his share, he needs to find a nice way to get the money before Tom’s nasty instincts get the best of both of them.