Starship Troopers is set in the 23rd century, a time when Earth exists as a federation exploring other planets for colonization. In one of their exploration, humans find planet Klendathu, a world inhabited by insect-like creatures called Arachnids or “Bugs.” The arrival of people on their planet disturbs these creatures and they start wreaking havoc to ward off the people.
In the human federation of the earth, citizenship is only awarded to people who have done service to the army. As a citizen, a person is given luxuries exclusive to people with such status. A group of friends from Buenos Aires comprised by John “Johnny” Rico, Carmen Ibanez, Carl Jenkins and Isabel “Dizzy” Flores join the Federal Service after their graduation. After their enlistment, they are assigned to different units. Carmen is assigned to pilot the Rodger Young while Carl is headed for the Military Intelligence. Rico decides to join the Mobile Infantry, finding out that Dizzy has also joined the ranks to be near him.
The Mobile Infantry Training is supervised by Career Sgt. Zim. During their preparation, Rico becomes the squad leader and friends with another trooper named Ace Levy. He also receives a letter from Carmen informing him that she will be working under Rico’s former rival, Zander Barcalow. Not long after, a live-fire training causes the lives of Rico’s colleagues and his demotion. The incident makes him resign from his duties but before he can inform his parent about his resignation, an asteroid launched by the Arachnids destroys Buenos Aires, annihilating millions of people including Rico’s family. Because of this, Rico sets aside his resignation and rejoins the infantry to fight the Arachnids.
The infantry’s first attack on Klendathu does not turn out well. A lot of troopers are killed and heavily injured. Rico receives mortal wounds and is presumed dead by Carmen. He, together with Ace and Dizzy, is transferred to the “Roughnecks” headed by Lt. Jean Rasczak, Rico’s former high school professor. A rescue mission from Planet “P” turns out to be a trap when they discover the Arachnids waiting for them in an outpost. Rasczak’s legs is bitten off by an Arachnid and Rico kills him in mercy. Dizzy is also attacked and she dies in Rico’s arms before Carmen and Zander arrive to provide back up.
At Dizzy’s funeral, Rico and Carmen are reunited with Carl. Car informs them of their theory about the Arachnids. The military has reason to believe that there exist a sentient and intelligent “brain bug” that controls the other bugs. Carl also believes that this leader bug is capable of studying and analyzing the behavior of humans. He assigns Rico to be the new leader of the Roughnecks and gives him orders to go back to Planet P and apprehend the “brain bug,”
As the fleet of spaceships heads for Planet P, the bugs destroy Carmen’s ship. She and Zander escape using a pod but they crash into a tunnel system filled with bugs. Rico leads a rescue mission to save the two with Carl psychically helping them to get through the tunnels. They reach Carmen and Rico just as the brain bug sucks the brains out from Zander’s skull. When the brain bugs is about to drain Carmen’s skull, she cuts its proboscis with the knife that Zander secretly handed to her. Rico threats the intelligent bug with a nuclear bomb in order to escape. As they make their way out through the tunnels, they are ambushed by a swarm of bugs and their colleague Watkins sacrifices himself to save them. Upon their return, they find out that the brain bug has been captured and the military now plans to study it. The movie ends with a commercial showing Carmen, Ace and Rico as they encourage the viewers to join the Federation military service.