A 12th-century wizard's search for the alchemists' fabled stone results in the transposition of Stephen, a rock-collecting American boy, to the medieval Castle Mordemagne, where he becomes involved in Sir Egbert Bors Sauvepeut's efforts to scrape up the payments due his liegelord Geoffrey de la Roche. Stephen's stone fails to produce gold, but it does reveal the radiant nobility of Mig, the sorcerer's apprentice, and the sojourn ends to everyone's satisfaction when Sir Geoffrey agrees to take Mig for training in knighthood as his payment. There's no transmutation in the telling, either, or any metaphysical dimension, but as tourist class time trips go, this one offers a smooth enough ride and some moderately diverting stops.