 After a violent combat against the bugs in their planet, with many casualties of humans under the command of a coward officer, a group of troopers looks for shelter in an abandoned military post. The psychic Pvt. Lei Sahara (Colleen Porch) finds and releases Capt. V.J. Dax (Richard Burgi), who was left behind locked in a cell by his troop, after killing a general. Dax and two privates, in a daring mission, save Gen. J. G. Shepherd (Ed Lauter) and some soldiers from an attack of the bugs, and Shepherd gives him a command position. While waiting for rescue, some troopers are invaded through their mouths by small bugs that took control of their brains. When Gen. Shepherd is possessed by one creature, Dax and Sahara try to prevent him getting back to the Federation.