American investment banker Ben Hartman is on a vacation trip to Switzerland when a childhood friend approaches himandpromptly tries to kill him. Narrowly surviving the attempt on his life, Ben discovers that the body of his former friend—as well as all evidence of the confrontation—has disappeared. But this is just a beginning. Anna Navarro, a U.S. government agent, is sent to surreptitiously look into a string of deaths and murders of old men around the world. The only thing the men have in common is an OSS file marked with the code word SIGMA. Brought together by accident, Hartman and Navarro must uncover the secrets long-buried under the name SIGMA. At stake are not only their lives and the lives of everyone they hold dear, but the very future of the world.