Mind Guest

Diana Santee woke to find herself helpless in a starcraft bound for nowhere with all its controls destroyed. Beyond all known space she was saved by the secret outpost of an undiscovered star federation. They needed a woman like her for a desperate mission on a medieval world they were secretly probing. She fit the bill; she volunteered in gratitude. But when she became the unwanted mind guest of a terrified virgin princess it went beyond anything her space agent training had prepared for her. For she had been betrayed into the clutches of a slavery out of the darkest days of a primitive past. (from the back cover of the DAW Books first edition)