Military enlistees fight off an invasion by alien insects.

Upon graduating school, Johnny Rico volunteers for the Mobile Infantry to do his Federal Service. Far from having patriotic motives, Johnny has joined the infantry to win the heart of his girlfriend, Carmen Ibanez, who has signed up for the Fleet Academy to become a starship pilot. Johnny undergoes rigorous military training at boot camp along with other young recruits including Dizzy Flores, who has harbored a crush on Johnny from their school days, and Ace Levy who earns Johnny's respect and friendship. Johnny accepts the challenge of boot camp and displays remarkable abilities that eventually earn him the position of squad leader. When a tragic training accident occurs on his watch, Johnny realizes he joined up for the wrong reasons. He is about to resign when Earth is attacked by the Bugs. Horrified by the death of his family and friends, Johnny is on board when the Mobile Infantry travels to distant planets to take the war to the Bugs.