Doorways

Dr. Thomas Mason had a regular life, with a regular job, and a regular girlfriend. Until one night, zapped from somewhere else, a mysterious young woman named Cat ends up in his E.R. Pursued by the government and twisted creatures from her own world, Cat inadvertently embroils Tom in her quest for freedom. Which takes him to alternative Earths he never imagined - and which he may never get back from! Features a new introduction by George R. R. Martin.