The wall of the library between the bookshelves was, indeed, paneled in dark wood, like the doors. But there was little enough of this surface, because the built-in bookshelves took up so much space. With the aid of the library ladder it took Mary and John comparatively little time to go over every inch of the paneling very carefully, thumping the wall with the heel of Mary’s slipper, to see if it might be hollow. But no sound betrayed a secret hiding-place. No scratch or knot concealed a tiny keyhole. Tired and disgusted at last, they gave up the search. “I think that’s a pretty poor joke!” said John. “A key without anything to fit it to is about as silly as can be!” “Aunt Nan made some silly jokes in other parts of the house,” said Mary. “But she hasn’t done so in the library. I don’t believe she meant to tease me. Let’s go and tell Father. Perhaps he will know what it means.” And forthwith they tripped to the Doctor’s study, with the key and the lantern and the marked copy of “Midsummer Night’s Dream,” to puzzle the Philosopher. They laid the three exhibits on his desk, and stood off, challenging him with eager eyes. Dr. Corliss looked at these things critically; then he followed them back to the library and glanced about the walls. “Well, Father?” asked Mary at last. “What do you think it means?” The Doctor hummed and hawed. “Why, I think it means that Aunt Nan was playing a joke on _you_ this time, Mary!” he said, laughing. “It would be just like her, you know. You can’t hope to be the only one to escape her humors. Besides, this key doesn’t look to me like a real key to anything. You mustn’t expect too much, my girl, nor get excited over this legacy of yours, or I shall be sorry you have it. I suspect there are no more gold watches and hundred-dollar bills floating around in your library. It wouldn’t be like Aunt Nan to do the same thing twice. It was the unexpected that always pleased her. You had better make the most of your books for their own sakes, Mary.” “Yes, I am going to do that,” said Mary, taking the key from her father and putting the green string around her neck. “I am going to wear it as a sort of ‘Midsummer Night’s Dream’ charm. And I believe that some day I shall find out the key to the key, if I look long enough.” “If you read long enough, perhaps you may,” said her father, laughing. “I have heard that they find queer things in Shakespeare sometimes--ciphers and things like that. But I never had time to study them up. A cipher is _nothing_ to me.” And he chuckled at his little joke. “If I read long enough, perhaps I may find out something. That’s so!” said Mary. “I’ll keep on reading.” “Pooh! That’s a slow way!” said John. “If there was anything in _my_ library, I’d want to find it out right away!” “If she has put anything in my library, that isn’t the way Aunt Nan meant me to find it,” retorted Mary. “I am going to do what Aunt Nan wanted, if I can discover what that is.”