From an alternate world, the Warden opens a portal to Earth in order for a human to perform predator control and destroy the Harn, a tick-like alien creature that creates offspring. This alien being is affecting the natural ecology of World 7 and must be removed. Ed Brown, an older trapper, starts settling into his winter cabin, unleashing his cat, old Tom, onto the huge amounts of mice that had proliferated there over the summer. A few days later, a portal into another world opens near the trail by the boat landing. Ed inspects it, pokes at it, and shoots some tobacco spit in, but does not go in. The next day, he sets up an alarm in order to know if any creature comes through the hole, then continues on with his chores. A small, hooved creature sets off the alarm while coming through the portal, which Ed kills and feeds to Tom. This continues to spur his curiosity about the other world, until he finally decides to go in. Heavily armed, he explores the new world all while being closely followed by the Harn. He shoots and kills a few alien creatures and catches a glimpse of the Warden before returning home to his cabin. He reflects on his exploration and decides to hunt and sell alien fur, as it would be more lucrative. In a pair of snake-proof pants, Ed starts hunting in World 7, and during one of his trips, he discovers the lair of the Harn. Finally, the Harn gets enough of him and mounts an offensive against him, coming through the portal and trapping him in his cabin. As most of the Harn is hunting in the woods around the cabin, Ed makes a run for the portal in order to burn the part of the Harn that is in its lair. With the Harn dead, the Warden appears and communicates his approval of his actions with Ed. Ed returns home. The portal disappears and life as normal resumes.