Five years after the still unexplained event that altered the world, killing millions, the residents of what is now known as Tower Island, go about their lives with an uneasy, but confident feeling of safety. The zombies, or 'crits' as they have become known, are no longer a danger to the community, thanks to the efforts of Captain Evan Stewart and his troops. But something strange about the crits recent behavior has him on edge. Though the crits are massing near the gate, they make no effort to gain access to the island.
Attending a party in the elite Tower, a twenty-six story apartment complex, Evan notices muzzle flashes near the perimeter gate on the causeway leading to the island. Fearing an attack, he attempts to contact his troops, but finds the breach has reached to the island, crits are roaming the streets. Unable to reach the island defense forces, Evan tries to get to the ground to lead the fight, but discovers the Tower is already overrun.
Unarmed, with thousands of somehow organized crits between him and escape, Evan must find a way to lead the tower residents to safety. As the muzzle flashes of his troops diminish, he realizes the battle is lost—no help will be coming. With the tower overrun, Evan decides there is only one way down. They must descend the tower from the outside.
After a narrow escape from the Tower, a twenty-six story apartment building, overrun with living dead, known as crits, and leading forty people to safety, Evan Stewart returns to the island in search of any last survivors. Concerned with the organized way the crits attacked the island, Evan approaches with caution and observes the crits. At first, they look to be doing what they always did, wander aimlessly in search of human flesh to devour, but as he watches, he begins to notice patterns in their behavior as if their actions have been thought out and planned. Were the crits evolving into thinking entities? If so, that made them more dangerous and deadly than ever and he fears for the survival of the human race. Sneaking on to the island, Evan finds survivors and works to get them safely away, until he discovers that the Island Defense Force, of which he is a Captain, has been feeding survivors to the crits to eliminate the human presence. Their ultimate goal is to take over the island for themselves. Once all humans are gone, they plan to systematically wipe out the invading crits. However, they greatly underestimate what the crits have become and an all out battle for survival ensues. Caught between the Force and the crits, Evan must find a way off the island leading a small group of men, women and children, before they are either gunned down or become food.