sky 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."

"Maybe," answered Tom absently, for he was reading the missive. "I
say!" he suddenly cried. "This is great! A clew at last, and from St.
Petersburg! Listen to this, Ned!

"This letter is from the head of one of the secret so