In ancient China, a group of European mercenaries encounters a secret army that maintains and defends the Great Wall of China against a horde of monstrous creatures.

Life for former United Nations investigator Gerry Lane and his family seems content. Suddenly, the world is plagued by a mysterious infection turning whole human populations into rampaging mindless zombies. After barely escaping the chaos, Lane is persuaded to go on a mission to investigate this disease. What follows is a perilous trek around the world where Lane must brave horrific dangers and long odds to find answers before human civilization falls.