A shapeshifting alien -- code name Spartan -- reaches Earth with dire plans for civilization. Corbet Tomms, a freespirited loner troubled by psychic visions, is recruited by a secret agency to hunt down the creature. With the help of his no-nonsense FBI handler, Aggie Rittenhouse, Corbet tracks the murderous alien. But he soon realizes that Spartan is at the heart of his most terrifying vision, one that portends global disaster. Spartan must be found before it activates a freakish weapon that will forever alter what it means to be human.