Francis Patcham wins a scholarship to an exclusive school in an old castle where he becomes entranced by Latin and Ancient Greek. When in the restricted section of the old Library he falls through a swinging bookcase door and arrives in a medieval apothecary, within the same castle, but at least 200 years back in time. He is swept up into becoming an apprentice, learning ancient medicine and it seems he cannot return to his own time unless the moon and stars align in the same way. Then there is something more he must do to make it all work. Francis finds he must make a choice.