What's the Worst That Could Happen?, Hardcover/Donald E. Westlake

With the planned heist of a religious relic, Dortmunder, the unluckiest criminal in the world, plunges into international diplomacy with a caper for acquiring a seat on the United Nations General Assembly. But a major fiasco proves a bone of contention and forces him to come up with Plan B. Dortmunder's lucky ring is stolen in the bungled burglary of a nasty billionaire's Long Island mansion. Now, a series of raids are planned to get the ring back -- and get even.