Grumbletooth's Riddle

Under the stairs there was a voice. “What has keys but no locks, space but no room?” The child answered: “A piano.” The voice grunted. The next morning the lost ring was on the step. So it went: a riddle, an answer, a small reward. Get it wrong and the milk would sour. Get it right and something would be returned. See Grumbletooth for the full profile.