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In an attempt to colonize Mars, 21st century scientists are tasked with terraforming the planet. Their goal is to seed the planet with a modified algae to absorb sunlight and purify the atmosphere, and cockroaches, whose corpses spread the algae across the planet as they feed. Five hundred years later, the first manned ship to Mars lands and its six crew members are attacked by giant mutated humanoid cockroaches with incredible physical strength, later labeled "Terraformars"; the crew is wiped out after sending a warning back to Earth. Two years later, BUGS II, a multinational expedition of genetically modified humans, is sent to collect 10 samples of both sexes of roaches, and exterminate the mutated bugs to take control of the red planet. Only two survivors manage to return to Earth, one swearing to return and avenge their fallen companions. As a third expedition is assembled questions are raised about the true origin of the Terraformars and their connection with an unknown disease afflicting mankind, the Alien Engine Virus, or A.E. Virus. To fight the Terraformars' strength and agility, members of the second and third expedition undergo genetic modification to inherit the characteristics of other organisms, only possible after having a special organ implanted with a 36% chance of surviving the surgery itself. The third expedition ends with most of its crew members killed as well, be it by fighting the Terraformars, or amongst themselves in the multi-sided conflict between the various factions aboard the ship, each with own opposing interests. Despite that, the few survivors manage to collect enough samples for the research on a cure to the A.E. Virus and return home. However, a new fight against the Terraformars begins when it is revealed that the creatures arrived on Earth long before, and after multiplying on an alarming rate and adapting themselves far better to their new environment than they did to their homeworld, they start their plan to take over the planet.