George Rr Martins Doorways

"Doctor 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. A quest that takes him to alternative Earths he never imagined... and from which he may never return!"