What's the Worst That Could Happen? by Donald E. Westlake

When billionaire hotshot Max Fairbanks, who has caught Dortmunder burgling his Long Island estate, tells the arresting police that the good-luck ring on Dortmunder's finger was stolen from him (when it was in fact a gift from Dortmunder's girlfriend, May), Max's fate, no matter how well protected he may be, is sealed.

Dortmunder makes repeated attempts to get his ring back, hitting on ingenious ways to get into the billionaire's lavish Times Square and Watergate apartments, making off each time with considerable more loot with each heist. But while Dortmunder is not unhappy with the loot he is really after only the ring. It's a pride thing.

When Fairbanks goes off to his huge casino/hotel/theme park in Las Vegas, in a deliberate attempt to entrap Dortmunder, does the dour vengeance-seeker shift into really high gear. Other friends from previous Dortmunder outings are collected into a formidable army, pitted against the best security Max's millions can buy, all leading to a showdown only Westlake could have conceived.

Fabulous! This is the most elaborate heist ever! Plus we get to see everyone travel, by bus, by air and by motor home! Kelp finds his own lady friend, Anne Marie, whom he picked up in New York while he was helping Dortmunder break into Fairbank's apartment. Anne Marie who was drowning her sorrows in the bar after her husband left her to go back to Kansas quickly jumps in to lend a hand. She has a knack for it too. Can't wait to read more of this fun, fun, fun series.