When a childhood friend unexpectedly attempts to murder him in Switzerland, an American investment banker begins to unravel a mystery involving his famous financier father and a mysterious OSS case code-named Sigma.
The first message sent to Tom Thorne's phone was just a picture - the blurred image of a man's face, but Thorne had seen enough dead bodies to know that the man was no longer alive. But who was he? Who sent the photograph? And why? While the technical experts attempt to trace the sender, Thorne searches the bulletins for a reported death that matches the photograph. Then another picture arrives.