L. Sprague deCamp 
Hostage of Zir [EPUB ebook] 

Outside the walls of the starport Novorecife, Earthmen on the warrior planet Kishna are on their own. So when he is chosen to lead the first ersuma (Earth-tourists) through the sorcerer-kingdoms of this "protected" medieval world, Fergus Reith must first learn to speak Durou; must take the chemical oath against imparting technical information; and must above all else learn to handle a broadsword! All these skills are needed when Reith finds himself and his ersuma trapped as pawns in a deadly war between a sorceress and a sterile kingdom under three moons . . . The Hostage of Zir is the third of L. Sprague de Camp’s Krishna book — interplanetary romance in the tradition of Edgar Rice Burroughs’ Martian Tales.