"Semi-Autonomous World Troy"
The men of 1st Marine Combat Force are in a life-and-death struggle with the Dusters, bird-like aliens who launched a surprise attack on Troy, and vanished the entire Human population. When Corporal John Mackie and his squad from India Company aren't fighting off "human wave" attack after "human wave" attack, they are aggressively patrolling in search of the Dusters, intending to meet and destroy them in their own bases.
In space, the remnants of Amphibious Group 17 rescue soldiers and sailors from wounded Navy starships. They begin feeding small, reassembled units to the surface of Troy. As they make planetfall, the soldiers have their first contact with the Dusters even before they reach their target firebase. Soon after, they are engaged in the same kinds of defensive and offensive operations as the Marines.
On Earth, the president of the North American Union orders the formation of a field army to be dispatched to Troy to aid the badly outnumbered Marines and soldiers, but have they any hope of arriving in time?
Things seem grim for Troy and its defenders as a new Duster fleet arrives and attacks the remaining warships of Task Force 8, in orbit before landing a huge invasion army meant to defeat the Human forces.