Free Vale of the Vole by Piers Anthony

Fragments of glass flew out, and the other ogre was gone. Esk stood before a man-sized frame from which jags of glass projected.
    "It was a mirror!" Chex exclaimed. "Except—"
    Esk's ogre nature left him. As he returned to the human condition, his intelligence increased, and he understood. "A reverse mirror!" he said. "It showed only the other side of me—the side that I wasn't. So when I was a man, it was my ogre self, and when I turned ogre, it turned human. Only I was ogrishly stupid and aggressive, and broke it when I didn't have to."
    Chex approached. "I don't think it was just a mirror," she said. "Vol-ney and I saw it too, and it looked and sounded like a real ogre. Your state may have governed it, but it was real enough in its fashion. Like the illusion of the mountain, it was enough to do the job. If you hadn't cowed it—"
    Esk shrugged. "Maybe so. Certainly it was my challenge, not anybody else's. This one wasn't let out early!"
    "It wasn't alive," she pointed out. "The inanimate challenges remain in place; only the dragons are loose, and maybe whatever other animals were supposed to be used."
    "It wasn't alive, so it didn't leave," he agreed, understanding. "So we still don't know whether anyone is in charge of the challenges. I don't like this."
    "Neither do I," she said.
    "Unlew thiv iv the challenge?" Volney suggested.
    Chex paused thoughtfully. "This mystery? This is the true challenge? Meant for all three of us to solve, together?"
    "I do not know, I only guew," the vole said.
    "It is a most interesting conjecture," she said. "We knew to expect the unexpected, and that's about as unexpected as anything could be. It seems reasonable to conjecture that a more sophisticated challenge would be required to handle three dissimilar querents simultaneously."
    "But why should there be three at once?" Esk asked. "We would have come separately, if we hadn't met on the paths."
    "True. It does seem largely coincidental." She quivered her wings, pondering. "Is it possible that our missions are linked? That we did not arrive coincidentally, but that the three of us are destined to cooperate in some greater endeavor so that a single answer will serve us all?"
    "But you knew nothing of the Kiw-Mee River," Volney protested.
    "Yet Esk did encounter the sultry demoness from that region," Chex pointed out. "So his mission may have a common motivation with yours. I confess, however, that my own mission does not seem to connect. I think this is too speculative to be taken as fact, at least at this stage."
    "Maybe the Good Magician will tell us soon," Esk said.
    "Maybe," she agreed, but she seemed dubious.
    They proceeded on into the castle proper. It was silent; no more challenges manifested.
    "Halooo!" Esk called. "Anybody home?"
    There was no answer.
    They passed into the residential section of the castle. This should be beyond the region for challenges, ordinarily, but no one met them. "Maybe they stepped out for a bite to eat?" Esk suggested facetiously, but the humor, if any existed, fell flat.
    They walked through chamber after chamber. All were cluttered with artifacts of magic and household existence; none had living folk. In the kitchen was a table with a petrified cheese salad in the process of composition; evidently the Gorgon had been making it when she abruptly departed. The greens were hardly wilted; she could not have left more than a day before. In a bedroom were toys and bins of assorted fruits: evidently the work of the Magician's son Hugo, who Chex had heard could conjure fruits. But no sign of the boy. Upstairs, in a crowded cubby of a study, was a high stool by a table with a huge open book: the Magician's Book of Answers, over which he was said to pore constantly. But no sign of the Magician himself. There was even a marker, showing the particular bit of information he had been contemplating; it seemed to relate to
    the aerodynamic properties of the third left central tail feather of the midget roc bird.
    "I