Donald Westlake, What's the Worst That Could Happen? (1997)
As an ebook:
Mysterious Press (2012)
The answer to the question in the title of the book is "You don't want to know."
Dortmunder's companion, May, receives a ring from her cousin, as May's part of the "estate" of an uncle. Dortmunder likes it and begins wearing it. The first thing that happens is that Dortmunder and a colleague find a householder at home when they go there to liberate some things. The colleague fades away, but the homeowner, Max Fairbanks (a billionaire industrialist), who was unexpectedly at home, calls the cops and nabs Dortmunder. And, once the cops arrive, Fairbanks claims that the ring is actually his, and takes it from him. From there on, Dortmunder tries and tries to recover the ring, and strange things ensue. But Dortmunder and the gang make out better than they usually do, and order is restored to the universe. I can't believe I hadn't read this one before.
That's not to say there are no flaws. The corporate bankruptcy morphs into a personal bankruptcy. The NYC cop who arrests Fairbanks in Las Vegas (well, technically, the Vegas cops do the collar) has signed extradition papers--that's not how extradition works. And Fairbanks seems more like the head of a sole proprietorship than of a corporation, Not withstanding this, a joy to read.