The authors' first and bestselling thriller, The Relic, hit the lists in part for its clever exploitation of an extraordinary setting--the American Museum of Natural History. Just so, their fourth novel (after Reliquary) makes sprightly use of Nova Scotia's Oak Island and its notorious Money Pit--here transplanted to offshore Maine as the Water Pit on Ragged Island. The novel opens with a brisk recap of often fatal efforts over the past 200 years to recover a fabled treasure--now worth $2 billion and including a mysterious relic, St. Michael's Sword--hidden by English pirate Edward Ockham in the Water Pit. The difficulty is that the Pit, nearly 200 feet deep, was designed to flood and to kill through booby traps anyone trying to broach the treasure. Into this nifty setup steps Martin Hatch, returning to Ragged Island 25 years after his brother and father died in the Pit. Hatch is back as part of a massive expedition attempting a high-tech assault on the Pit. Brash melodrama ensues as expedition members suffer various gory accidents and as Hatch realizes that the Sword possesses a quality that may kill the entire expedition. The novel suffers from a diffusion of villains--the authors variously demonize the Pit, the Pit's designer, the crazed expedition leader and the Sword--and from workaday prose and assembly-line characters (a computer nerd, a sexy French archeologist, a righteous minister). Machine-gun pacing, startling plot twists and smart use of legend, scientific lore (including cyptanalysis) and the evocative setting carry the day, however, resulting in an exciting boys' adventure tale for adults that's bound to be one of most popular of the summer reads. Film rights optioned by Arnold Kopelson; foreign rights sold in eight countries; simultaneous Time Warner audio. (July) FYI: The mystery of Oak Island and its Money Pit has been detailed in several books (e.g., D'arcy O'Conner's The Money Pit, 1978). The Pit, target over the past two centuries of numerous failed expeditions costing millions of dollars and six lives, is variously rumored to contain Captain Kidd's treasure, Incan gold and even the Holy Grail.