"Of course, the story everyone thinks of is the one concerning the Piper of Hamelin. It was in the year 1284. The rats were thick, and the Piper agreed to lead them out of the town for a certain sum. He played a pipe, no doubt some kind of flute, and the rats followed him. When the people refused to pay, he returned on the 26th of June, the feast of Saints John and Paul, and again played on the pipe. This time the children, one hundred and thirty in number, followed him into a cave and were lost. The date is well documented. A number of historians believe that it actually occurred, and on the gate of the town is the statement. "'_CENTUM TER DENOS CUM MAGUS AB URBE PUELLOS DUXERAT ANTE ANNOS CCLXXII CONDITA PORTA FUIT._'[1] "The same story is found, with variations, in all parts of the world. There is, for example, the story of the wicked Hatto, abbot of Fulda. He was visited by a swarm of rats who killed him. I can give you a dozen variations of that story, but in each of them the rats came and went, suddenly, as Mr. Willowby says they have been doing in New York." "I should like to see a few examples of this mass movement of rats. I saw a lemming migration in Norway, but that was different," explained Rastell. "It seems to me that if we actually saw one of these nocturnal attacks, we might learn why they wanted to do it." "He is deadly right," agreed Professor Wilson. "A few actual facts are worth a hundred theories." "That is why I have asked you to help me," explained the richest man in New York. "I have prepared some experimental stations for your use. I can put you in a grocery warehouse and guarantee that inside of a week you will see more rats than you ever dreamed of. I have a laundry and a small hotel. We can work out the details right now. All I am asking of you is to find out, when the rats come, _why they come_ and, once we know that, we can do something to solve this problem." "The game looks interesting," declared the Professor of rat psychology. "What I am interested in is why the rats do it. I am sure that it is because they want to do it, but are they forced to want to do it? It is a problem that will take a lot of research to solve, but Rastell and I can solve it. With all respects to our friend, Mr. Crawford, I think that he had better stay away and just keep on reading about his little pets. A few thousand vicious rats would be hard for him to deal with." "I guess you are right," laughed Winifred Willowby. "Crawford and I will stay here and read about it while you two do the actual scientific work. By the way, Crawford, in that story of the Piper, what was given the credit for drawing the rats out of the town?" "The tune that he played on the pipes!"