Three books in one! Joel Rosenberg's Guardians of the Flame: The Warriors is an omnibus edition published in 1985 that collects the first three novels of the Guardians of the Flame fantasy series. The book is a work of "portal fantasy," in which a group of college students is transported from their world into the bodies of their characters in a role-playing game. 
 
The series begins with a group of college students playing a fantasy role-playing game led by their philosophy professor, Arthur Simpson Deighton. He mysteriously sends them into the game's world, Pandathaway, where magic is real and slavery is widespread. Trapped in this new land, the students must now inhabit the roles of their game avatars and find a way to survive.