The Doomsday Conspiracy by Sidney Sheldon

Commander Robert Bellamy of US Naval Intelligence is dispatched on a top secret mission. A weather balloon carrying sensitive military information has crashed in Switzerland. Bellamy must locate the ten witnesses to the incident so that they can be sworn to secrecy. \n\nBut as he conducts his search Bellamy begins to suspect that he, too, is being hunted, by an unknown lethal force, that what he was told about the balloon was only one part of an almost unbelievable happening... \n\nFrom Washington to Zurich, Rome and Paris, the story unfolds to reveal Bellamy's past: why the women he loves the most cannot return his love, why his friends become his deadly enemies, and why the world must never learn the incredible secret hidden on the Swiss Alps...