Starship Troopers is the story of Juan "Johnnie" Rico, a Filipino soldier in a futuristic spacefaring Earth military unit called the Mobile Infantry. Told in flashbacks, Rico's story is one of intense violence, taking place during a war with a race of sentient insects from another world. The novel spends a great deal of time reflecting from a Conservative point of view on war, service, nationalism, and other pertinent issues.
Starship Troopers takes place in the midst of an interstellar war between the Terran Federation of Earth and the Arachnids of Klendathu. It is narrated as a series of flashbacks by space marine Johnny Rico, a member of the "Mobile Infantry". This is one of just a few Heinlein novels set out in this fashion. The novel opens with Rico aboard the space corvette Rodger Young (named after Medal of Honor recipient Rodger Wilton Young), serving with the platoon known as "Rasczak's Roughnecks" (named after the platoon leader, Lieutenant Rasczak); about to embark on a raid against a colony inhabited by "Skinnies" (allies of the Arachnids). Rico himself is a 'cap [capsule] trooper' in the Terran Federation's Mobile Infantry.
The raid itself is relatively brief: the Roughnecks land on the planet, destroy their targets, and retreat, suffering two casualties in the process (one, Dizzy Flores, dies during the return to orbit). The story then flashes back to Rico's graduation from high school, where the reader sees his close relationship with his best friend Carl and their decision to sign up for Federal Service together over the objections of Rico's father. This is the only chapter that describes Rico's civilian life, and most of it is spent on the monologues of two people: retired Lieutenant Colonel Jean V. Dubois, Rico's school instructor in "History and Moral Philosophy"; and Fleet Sergeant Ho, a disabled recruiter for the armed forces.
Dubois elucidates the book's moral position in matters of war; whereas Fleet Sergeant Ho's monologues examine the nature of military service, and his anti-military tirades seem primarily in contrast with Dubois. Later it becomes apparent that his attitude and display of truncated limbs are intended to scare off unmotivated applicants.
Interspersed throughout the book are other flashbacks to Rico's History and Moral Philosophy course, which reveal that the rights of a full Citizen (to vote and hold public office) must be earned through voluntary Federal service. Those who do not perform this Service retain the rights of free speech, assembly, etc., but cannot vote or hold public office. This structure arose ad hoc after the collapse of the "20th century Western democracies", brought on by social failures at home (among which appear to be poor handling of juvenile delinquency) and military defeat by the Chinese Hegemony overseas.
In the next section of the novel, Rico begins training at Camp Arthur Currie on the Canadian prairie. Five chapters are spent exploring Rico's experience there, under the tutelage of career Ship's Sergeant Charles Zim. Fewer than ten percent of the recruits finish basic training; the rest resign, are expelled, or die in training. One of the chapters displays Ted Hendrick, a fellow recruit and constant complainer, who is flogged and expelled for striking a superior officer (Sergeant Zim) during a simulated combat exercise. Zim does not offer this information to his superior, but Hendrick does. Another recruit, a deserter who murdered a baby girl while AWOL, is hanged by his battalion after his arrest by civilian police. Rico himself is flogged for negligent handling of his equipment during a simulated nuclear weapons drill. Despite this punishment and his own earlier doubts about his fitness to serve, Rico eventually graduates and is assigned to a unit in the Fleet.
During Rico's training, the "Bug War" has changed from border incidents to a full-scale war, and Rico finds himself taking part in combat operations. The war "officially" starts with an Arachnid attack that annihilates the city of Buenos Aires (which kills Rico's mother). Rico briefly describes the Terran Federation's disastrous defeat at the Battle of Klendathu, during which his first unit and ship are destroyed. Following Klendathu, the Terran Federation is reduced to hit-and-run raids similar to that described at the beginning of the novel. This part of the book describes the daily routine of military life, as well as the relationship between officers and non-commissioned officers (personified in this case by Lieutenant Rasczak and Sergeant Jelal). Eventually, Rico becomes a career soldier, and one of his fellow troopers recommends him to Officer Candidate School, where he undergoes a second course of training. En route from the Roughnecks to OCS, Sergeant Rico encounters his estranged father, now Corporal Rico, in transit, and reconciles with him.
Sergeant Rico is commissioned a temporary third lieutenant for his final test: a posting to a combat unit. Under the tutelage of his company commander, Captain Blackstone, and the aid of his platoon sergeant, Zim (reassigned from Camp Arthur Currie), Rico commands a platoon during 'Operation Royalty': a raid to capture members of the Bugs' 'brain caste' and 'queens', and graduates as a second lieutenant. The final chapter serves as a coda, depicting Rico aboard the Rodger Young as the commander of Rico's Roughnecks (previously Rasczak's Roughnecks), preparing to invade Klendathu, with his father as senior NCO.