In a post-apocalyptic world where most of the Earth has been turned into desert wasteland inhabited by giant mutated bugs and humanity has been reduced to small cities and colonies due to the explosion of a bomb, a young man who calls himself Max the Bug Slayer wanders the wasteland constantly fighting and shooting the bugs for fun, until one day he stumbles across a garden being taken care by a young woman named Maisy Chambers. Max offers himself to follow and protect Maisy until they get to her home, and thus they start travelling together across a series of environments such as a desert, an abandoned city, a swamp and various caves, all taken over by giant bugs. Meanwhile, they start to reveal a bit of their past to each other: Max lived with his father and brother until the bomb dropped and both died, leaving him alone in the wasteland; Maisy and her mother had a gardening business together, until her mother disappeared while looking for soils in the wasteland, also leaving Maisy alone. While in the caves, they find a locket that belonged to Maisy's mother, next to the lair of an Alpha Centipede, who Max calls Soot. Max explains he found Soot when it was small, and it was his best, and only, friend, until Soot grew larger and more aggressive, forcing Max to leave it behind in fear of getting himself hurt. Maisy says that the locket had a picture of herself in it but it has been taken out, so they go to Soot's cave in search of her mother and Max and Soot go into battle. Soot then tries to attack Maisy, and Max is sadly forced to shoot and kill it. Not having found her mother, Max and Maisy then embrace together as the soil grows grass and flowers from the nutrients in Soot's blood. In a post-credits scene, a mysterious woman, whose face is never shown, holds a picture of a young Maisy in her hand.