The Sword and the Chain — Joel Rosenberg

WARRIOR, WIZARD, DWARF, THIEF, AND MASTER BUILDER--all of them had chosen this world as their destiny, a realm where dragons were only too real and magic, not science, was the law of the land. Karl, Andrea, Ahira, Walter, and Lou knew there was no going back to twentieth-century America now. Instead they were stranded in a time and place where only healing spells and their own wits stood between them and the sharp, deadly edge of a slaver's blade.

But even if they could have returned home by some sorcerous trick, all of them would have refused the chance, bound by their pledge to bring this incredible realm the one treasure it lacked--freedom! But leagued against them in their fight were the entire forces of both the Wizards and the Slavers guilds. And, in this world where a wrong step or a twisted spell could transform friend into foe, how could Karl and his band survive long enough to fulfill their pledge?