The troopers of two starships have joined forces to terminate a massive bug attack at a Federation outpost. Before the mission can be completed and the survivors evacuated, one ship abruptly departs and goes inexplicably dark. The remaining battle-hardened troopers race to the rescue only to discover that the threat from the bugs is about to hit home.

Federation trooper Johnny Rico is ordered to work with a group of new recruits on a satellite station on Mars, where giant bugs have decided to target their next attack.