The Sigma Protocol - Robert Ludlum

In Zurich, Switzerland, American investment banker Ben Hartman has arrived on holiday when he chances upon old friend Jimmy Cavanaugh -- a madman who's armed and programmed to assassinate. In a matter of minutes, six innocent bystanders -- and Cavanaugh -- are dead. But when his body vanishes, and his weapon mysteriously appears in Hartman's luggage, Hartman is plunged into an unfathomable nightmare, and suddenly finds himself on the run.