"It's only their motor back-firing," cried Tom. "It's all right,
They're done for now, we'll leave them behind."

He was a true prophet, for with a continued rush and a roar the airship
of our friends opened up a big gap between her rear rudders and the
forward planes of the craft that was chasing her. The three men were
working frantically to get their motor in shape, but it was a useless
task.

A little later, finding that they were losing speed, the three police
agents, or spies, whatever they might be, had to volplane to earth and
there was no need for the Falcon to maintain the terrific pace, to
which Tom had pushed her. The pursuit was over.

"Well, we got out of that luckily," remarked Ned, as he looked down to
where the spies were making a landing. "I guess they won't try that
trick again."

"I'm afraid they will," predicted Mr. Petrofsky. "You don't know these
government agents as I do. They never give up. They'll fix their
engine, and get on our trail again."

"Then we'll make them work for what they get," put in Tom, who, having
set the automatic speed accelerator, had rejoined his companions.
"We'll try a high flight and if they can pick up a trail in the air,
and come up to us, they're good ones!"

He ran to the pilot house, and set the elevation rudder at its limit.
Meanwhile the spies were working frantically over their motor, trying
to get it in shape for the pursuit. But soon they realized that this
was out of the question, for the Falcon was far away, every moment
going higher and higher, until she was lost to sight beyond the clouds.

"I guess they'll have their own troubles now," remarked Ned. "We've
seen the last of them."

"Don't be too sure," spoke the Russian. "We may have them after us
again. We're over the land of the Czar now, and they'll have
everything their own way. They'll want to stop me at any cost."

"Do you think they suspect that we're after the platinum?" asked Tom.

"They may, for they know my brother and I were the only ones who ever
located it, though unless I get in the exact neighborhood I'd have
trouble myself picking it out. I remember some of the landmarks, but my
brother is better at that sort of work than I am. But I think what they
are mostly afraid of is that I have some designs on the life of, say
one of the Grand Dukes, or some high official. But I am totally opposed
to violent measures," went on Mr. Petrofsky. "I believe in a campaign
of education, to gai