When the Mobile Infantry defeats an infestation on Pluto, the world is united as the Strategically Integrated Coalition of Nations (SICON) declares war on the insectoids.
The main story focuses on a group of troopers known as Alpha Team – otherwise known as Razak's Roughnecks – who are headed back to Pluto after Operation Pest Control.
After destroying Bug City on Pluto, SICON sights a giant Transport Bug. This reveals that the Bugs are not native to Pluto. They track it to the planet Hydora, which orbits a star in the Constellation Virgo and encounter a Brain Bug, an intelligent Bug that controls the other castes so they won't go insane and destroy each other. The Bugs are planning to take control of the entire universe and won't stop until the human race is extinct.
SICON attempts to set up a base on the planet Tophet, inhabited by a species nicknamed Skinnies. The Skinnies, however, have been enslaved by the Bugs to mine Xylon, a precious mineral used for Transport Bugs. The Mobile Infantry are able to destroy the Control Bugs overseeing the Skinnies and free Tophet, but the victory costs them their comrade Carl Jenkins, who has been put into a state of mental trauma. The Skinnies soon enlist in SICON to fight the Bugs, mainly due to their lack of interstellar travel technology...
