George R. R. Martin's Doorways #1

Running from her captors, Cat ends up in the ER where Tom Mason treats her and earns her trust. Cat is taken by the Feds and Special Agent Trager persuades Tom to help them. Cat realizes that Thane is following her and escapes taking Tom with her. Both Thane and the Feds catch up with them and Trager loses his life helping them escape through a doorway to a parallel Earth. There Cat saves Cissy from bandits and Tom saves Jake Edwards's life after he is shot by bandits. That Earth's version of Trager dies helping Cat and Tom escape from the still pursuing Thane to another parallel Earth.