"Cat and Mouse" by Ralph Williams is a science fiction novelette published in 1959. When Alaskan trapper Ed Brown discovers a portal to another world, he unwittingly becomes caught in an alien experiment gone wrong. A deadly predator called the Harn has infiltrated the experimental planet, and Ed must face this shape-shifting creature in a desperate battle across two worlds. Armed with limited ammunition and backwoods survival gear, he fights to survive against an intelligent organism that adapts with every attack. (This is an automatically generated summary.)