Books like The Sigma protocol by Robert Ludlum

In Zurich, Switzerland, Ben Hartman, an American investment banker on holiday, encounters his old friend Jimmy Cavanaugh, who is possessed by a murderous program. Within minutes, six innocent bystanders and Cavanaugh are dead, yet Cavanaugh's body disappears and the weapon reappears in Hartman's luggage. Hartman finds himself on the run, pursued by an unseen threat. Across the Atlantic, Anna Navarro, a field agent for the Department of Justice in Washington, D.C., is called to investigate the sudden deaths of eleven men worldwide. All victims share a single connection: a secret file older than half a century, tied to the CIA and labeled with the puzzling codename "Sigma." As Navarro follows the thread, she encounters a relentless killer who seems one step ahead, while Hartman and Navarro must together uncover the hidden truths behind the Sigma codename, facing revelations that threaten everything they believe and confirm their darkest fears.

First publish date: 2001