Hybrid fighters merging human and alien technology. Massive cannon emplacements on the Moon and Mars. A planetary defense force with the finest military personnel ever trained. For two decades we've known the enemy would return. The nations of Earth have collaborated on a unified defense program designed to defend the planet. Yet nothing could prepare us for the immensity of their new assault, and only the courage and skill of a few brave men and women can hope to bring our world back from the brink of extinction.