PFC Rafer Pelham's platoon on Gamma station L-27 has been decimated by recent enemy attacks, leaving the depot in ruins, all of their defenses down, and minimal provisions for the remaining twelve Marines. While scrounging for food in a remote section of the depot, the men come across an old Istron robot. The device appears to be in working order, and they power it up.
The robot immediately warns of another enemy attack. The men scramble for cover, avoiding further casualties from the incoming assault. Soon after, the robot locates a downed supply freighter with enough food and supplies on board to keep the men alive for the next few weeks.
A few days later a new C.O. arrives at the station, Lieutenant Waylon Grimes. The men urge Grimes to request an evac, but Grimes stubbornly refuses, ordering the men to repair as much of the base as possible, and prepare for the next assault. The men comply, completing many of the repair jobs, but a subsequent attack quickly destroys most of their work.
The robot works tirelessly to aid the repairs, but despite its help, the men soon realize the base can't be saved. In order to get out alive, they're going to have to convince Lieutenant Grimes to let them go, which again he refuses to do. But the robot has another plan, and the men soon have to decide who their real leader is.