In the distant future, the Earth is at war with a race of giant alien insects.  Little is known about the bugs except that they are intent on the eradication of all human life.  But there was a time before war...

Upon graduating school, Johnny Rico (Casper Van Dien) 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 (Denise Richards) 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 (Dina Meyer), who has harboured a crush on Johnny from their school days, and Ace Levy (Jake Busey) 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 while on his watch, Johnny realizes that he joined up for the wrong reasons.  He is about to resign when the Earth is attacked by the Bugs, and the city of Buenos Aires -- Johnny's home -- is wiped off the map.  Horrified by the death of his family and friends, Johnny's grief turns to anger and he determines to stay in the Mobile Infantry and fight to destroy the insect threat to human civilisation.

The Mobile Infantry travels to distant alien planets to take the war to the Bugs.  

They are a ruthless enemy with only one mission: Survival of their species no matter what the cost...