"Of course you may." Mr. Christianson took them up narrow stairs that kept going up and up and up. Finally they reached the top. From here they could see the ocean in the distance. "This is almost as high as the tower in our forest," said Greta. "In olden times this tower was very useful," explained Mr. Christianson. "From here one could see an enemy when he was still miles away." "Denmark doesn't have any enemies now, does it?" asked Anna. "No, Denmark is one of the most peaceful countries in the world. It is almost eighty years since we have been at war with any other nation." After a while they went down to the library. Mr. Christianson led the girls past rows and rows of books, placed on shelves that reached from the floor to the ceiling. When they came to the farthest corner of the room he stopped and reached for the book of Andersen's Fairy Tales without even looking. "You see, I know just where it is." Then a worried look came on his face. "Why, I can't understand this," he said. "This book was here last night, for I showed it to some friends. And now it is gone." "Maybe someone has borrowed it," suggested Greta. "That is impossible, for I keep the library locked, and none of the servants has the key." "Maybe you put it back in the wrong place," suggested Anna. "I'm afraid that is impossible, too. You see I keep this book in a very special place because I prize it more than any other book that I own. I am always careful to put it back in this same spot." [Illustration: THE COURTYARD OF VOSBORG] "We'll help you look for it," offered Greta. So the three began searching one shelf of books after another. "I suppose Hans would say that one of the Nisser had taken it," said Anna jokingly, when they had gone about halfway through the shelves of books. "I wouldn't be at all surprised if one _had_ taken it," answered Greta quite seriously. They kept on looking for almost an hour. By this time Mr. Christianson was really worried. He finally called in all the servants and asked if any of them had been in the library that day. None of them had. The disappearance of the book had become a real mystery. "I should hate to lose this book more than any other book in the library." "Let's look once more on the shelf where it's supposed to be," said Anna. Mr. Christianson laughed. "But we looked there very carefully when we first came in." Anna wanted to look there again, so she ran down the long room to the special shelf. "Here it is!" she shouted. "Right here on the shelf where it is always kept." The others rushed up at once. "Well, this _is_ strange," said Mr. Christianson. "It wasn't here an hour ago, and no one has been in this part of the room since then." "Except maybe a Nisse," said Greta.