Tom Swift, seated in his laboratory engaged in trying to solve a puzzling question that had arisen over one of his inventions, was startled by a loud knock on the door. So emphatic, in fact, was the summons that the door trembled, and Tom started to his feet in some alarm. "Hello there " he cried. "Don't break the door, Koku " and then he laughed. "No one but my giant would knock like that," he said to himself. "He never does seem able to do things gently. But I wonder why he is knocking. I told him to get the engine out of the airship, and Eradicate said he'd be around to answer the telephone and bell. I wonder if anything has happened?"