If Jake Applesauer, the agent at the Waterville station, was surprised at seeing two youths drop down out of an aeroplane, and begin questioning him about some suspicious strangers that had taken the morning train, he did not show it. Jake prided himself on not being surprised at anything, except once when he took a counterfeit dollar in return for a ticket, and had to make it good to the company. But, to the despair of Tom and Ned, he could not help them much. He had seen the party, of course. They had driven up in the hack, and one of the men seemed to be sick, or hurt, for his head was done up in bandages, and the others had to half carry him on the train. "That was Mr. Petrofsky all right," declared Ned. "Sure," assented Tom. "They must have hurt and drugged him. But you can't tell us for what station they bought tickets, Mr. Applesauer?" "No, for they didn't buy any. They must have had 'em, or else they paid on the train. One man drove off in the coach, and that's all I know." As Tom and Ned started back to Shopton in the aeroplane they discussed what could be done next. A hard task lay before them, and they realized that. "They could have gotten off at any station between here and New York, or even changed to another railroad at the junction," spoke Tom. "It's going to be a hard job." "Guess we'll have to get some regular detectives on it," suggested Ned. "And that's what I'll do," declared the young inventor. "They may be able to locate Mr. Petrofsky before those spies take him out of this country. If they don't--it will be too late. I'm going to talk to dad about it, and if he agrees I'll hire the best private detectives." Mr. Swift gave his consent when Tom had told the story, and, a day later, one of the best detectives of a well known agency called on Tom in Shopton and assumed charge of the case. The early reports from the detective were quite reassuring. He got on the trail of the men who had taken Mr. Petrofsky away, and confirmed the suspicion that they were agents of the Russian police. He trailed them as far as New York, and there the clews came to an end. "Whether they are in the big city, which might easily be, or in some of the nearby towns, will take some time to learn," the detective wrote, and Tom wired back telling him to keep on searching. But, as several weeks went by, and no word came, even Tom began to give up hope, though he did not stop work on the air glider, which was nearing completion. And then, most unexpectedly a clew came--a clew from far-off Russia. Tom got a letter one day--a letter in a strange hand, the stamp and postmark showing that it had come from the land of the Czar. "What do you suppose it contains?" asked Ned, who was with his chum when the communication was received. "Haven't the least idea; but I'll soon find out." "Maybe it's from the Russian police, telling you to keep away from Siberia."