All that day they traveled, Tom and his chum keeping a lookout for the blue machine, but not seeing it. The young inventor had so laid his plans that before it got too dark he descended in a broad field on the outskirts of a big city. As the aeroplane was large enough to permit of sleeping in it and as Tom had brought along blankets, they decided to spend the night in the _Blackbird_. It was the next morning about nine o’clock, and just about the time Tom and Ned were taking off again on the second day of their trip, that Mr. Swift was summoned to the telephone in his office. “Dey’s somebody dat wants to talk to you ’ticklar like,” reported Eradicate. “Perhaps it’s a message from Tom!” exclaimed Mr. Swift. “He may have caught the robbers and gotten back his chest.” “No, sah, it don’t sound like Massa Tom,” said the colored man. The voice to which the aged inventor listened was not that of his son. Instead, over the wire came strange tones asking: “How much will you pay us for the return of your chest of secrets?” Mr. Swift was so surprised that he almost dropped the receiver. CHAPTER XXIII THE BLUE MACHINE BARTON SWIFT was the true father of his energetic son, and Tom inherited his qualities from his father. Which is to say that in his youth Barton Swift had been fully as active and quick as was now the young inventor. Though age and illness had to some extent dimmed and enfeebled the powers of the man, still it needed but this spark—that strange telephone message—to galvanize him into action. After the first shock of hearing so unexpectedly about the stolen chest of secrets, Mr. Swift was ready to take active measures to trace the voice coming out of the machine. “What’s that you say?” he asked, nerving himself to carry on an ordinary conversation about a most extraordinary topic. “Who are you and where are you?” “Don’t you wish you knew?” came back the challenging inquiry. “Are you ready to talk business?” “Of course I am,” answered Mr. Swift. “We want that chest back, and we’ll pay any reasonable amount.” “I’m not saying the amount will be reasonable,” was the reply, and emphasis was laid on the last word. “But you’ll pay our price or you don’t get the chest. And I warn you that if you try to communicate with the police or set the detectives on our trail we’ll immediately break off negotiations.” Trying to get in touch with the police was just what Mr. Swift was then doing. Ned Newton’s father had entered the office, and, seeing him, Mr. Swift at once took pencil and paper from his desk and while he talked in a rather general way with his unseen listener, he jotted down a few words, explaining matters and suggesting that Mr. Newton go to another telephone to learn from the central operator where the mysterious call was coming from.