Commander Keen's adventure on Planet Krisle begins after his BWB Megarocket is shot down by a swarm of robots. Forced to crash-land, he crawls from the wreckage of his ship to find himself in a swampy forest in the southwest of this new world.
After meeting one of the strange inhabitants of this land, Keen sets off into the night to find and destroy the being responsible for the robot invasion of the planet. The quest to defeat Atroxus will take him through dark mysterious swamps, a vast crystal cavern under a mountain range, primitive forest-lands, well guarded Atroxian bases, the gruesome ruins of Kridonea City, and eventually to the corrupted Sky Sanctum where Commander Keen's most dangerous enemy yet is waiting, ready to battle for control of Planet Krisle!
The entire Western region of Krisle is a swampland, thick with tall grey trees and lush green undergrowth. Much like Earth, Krisle seems to have a very watery surface with rivers and streams flowing throughout the landscape and nourishing the vast plant-life here, in many places flowing underground and carving out vast cave systems deep under the planet's surface. The Western swampland of Krisle is a wild and natural place completely untamed by any kind of civilization, and is home to many species of plant and animals which thrive in this environment.
A great mountain range dominates the South-East, heaved up from the ground through millions of years of geologic processes. Under these mountains there is an enormous cave which is formed from the crystalline rock that naturally occurs here. All sizes and colors of crystal can be found in this cavern, perhaps that could explain the extensive mining operation the Atroxians have set up here...
Krisle is home to all kinds of evolved life but one species has evolved to be as intelligent as Earth's Humans, perhaps even more-so. These bird-like beings call themselves the Krile. Kridonea City is their home, built in the north-east of the region. Constructed from quarried stone, the buildings in Kridonea are set atop tall pillars which hold each building high above the ground, and in the center of the city is the Great Ziggurat where the Krile elders meet to govern their people. These people, the Krile, were a kind and friendly race of alien being, peacefully inhabiting their beautiful city. And then the robot invasion began...
The Atroxian Realm
Approaching Planet Krisle, Commander Keen saw what appeared to be three massive hurricanes swirling over the surface of the planet. As he drew closer, he realized these are not hurricanes, but three massive swarms of robots! After being shot down by these robots, Keen learns that an evil being named Atroxus has invaded Planet Krisle with his robotic army, taking over the Krile temple known as the Sky Sanctum and using it's power to unleash a malevolent realm of Atroxian robots onto this peaceful world.
This invasion is destroying Krisle's environment and slaughtering it's people. Atroxus must be stopped and brought to justice, but who is bold enough to try? Who is brave enough to battle an entire realm of evil robots?
Commander Keen. That's who.