long to the same gang that Simpson, Blakeson, and Schwen are members
of--the German spies."

"But what was their object?" asked Ned. "Did they try to force you to
tell them the secrets of the tank?"

"No; and that's the funny part which makes me so suspicious," Tom
answered. "If they'd tried to force something out of me, I would
understand it better. But they just kept me a prisoner after taking
away what papers I had."

"Were they of any value?" asked Mr. Damon.

"Not as regards the tank. That is, there was nothing of my plans of
construction, control or anything like that, though there was some
foreign correspondence that I am sorry fell into their hands. However,
that can't be helped."

"And did they just keep you locked up?" asked Ned.

"That's about all they did. After the fight--and it was some fight!"
declared Tom, as he recalled it with a shake of his head--"they left me
here with the door shut. There must have been some one on guard, for I
could faintly hear somebody moving about.

"I tried to get out, of course, but I couldn't. That vault must have
been made to hold something very valuable, for it was almost as strong
and solid as one in your bank, Ned. The only window was placed so high
that I couldn't reach it, and it was barred at that.

"They opened the door a little, several times, to toss in once some old
bags that I made into a bed, and next they gave me a little water and
some sandwiches--German bologna sausage sandwiches, Ned! What do you
think of that--adding insult to injury?"

"That was tough!" Ned admitted.

"Well, I had to put up with it, for I was half starved, and as sore as
a boil from the fight. I didn't know what to do. I knew that you'd miss
me sooner or later, and set out to find me, but I hardly thought you'd
think of this place. They couldn't have picked out a much better
prison to hold me, for, naturally, you wouldn't suppose enough of it
was left standing, after my tank had walked through it, to make a
hiding place.

"However, there was, and here I've been kept. At last I thought of the
plan of sending out a message on the scrap of paper I could tear out of
my hat. So I wrote it, and after several trials I managed to toss it
out of the window. Then I just had to wait, and that was the hardest of
all. The last twelve hours I've been without food, and I haven't heard
any one around, so I guess they've skipped out and don't intend to come
back."

"We didn't see any one,"