A shape-shifting, indestructible robot—a "Type H-9 Ruum"—is accidentally left behind on earth during the age of the dinosaurs by visiting aliens, and not recovered because their ship is destroyed in a battle.
Millions of years later Jim Irwin, a uranium prospector in the Canadian Rocky Mountains, encounters the Ruum's specimens, animals which include modern and prehistoric mammals and a small Stegosaurus.
Safely in the plane, they make plans to bring a helicopter and collect some of the Ruum's specimens in its absence to sell to scientists.
Following the events of the original story, it is mentioned in passing that the Ruum succeeds in paralyzing a human (implied to be an ironic self-insert of Porges himself).
Mistaking the Ruum for an item of human technology they take it aboard, intending to present it to their Queen as an amusing novelty.
Back on their homeworld, the giant Queen is engaged in laying thousands of eggs that will hatch into soldier ants, the vanguard of an army that will conquer the galaxy.
"The Ruum" was selected by David Drake for his 1988 anthology Things Hunting Men, where he commented that this was one of Porges seventy-some "meticulously crafted stories" where "sometimes the problem the protagonist faces really is insoluble."