What they saw was that the grounds seemed to be surrounded, near
the wall, by heavy trees, which made it difficult to see much of
what was within. But in one place there was a break, so that,
looking across velvety green lawns, they could see a small part of
an old and weatherbeaten grey house. It appeared to be on a rise,
and to stand several stories above the ground, so that it might
well be an ideal place for the establishment of a heliograph
station.

But Harry's suspicions were beginning to take a new turn.

"I believe this is the biggest find we've made yet, Dick," he
said. "I think we'll find that if we discover what is really
going on here, we'll be at the end of our task -- or very near it.
It's just the place for a headquarters."

"I believe it is, Harry. And if they've been so particular to
keep everything about it secret, it certainly seems that there
must be something important to hide," suggested Harry, thinking
deeply. "I think I'll write a letter to Colonel Throckmorton,
Dick. I'll tell him about this place, and that we're trying to get
in and find out what we can about it. Then, if anything happens
to us, he'll know what we were doing, and he will have heard about
this place, even if they catch us. I'll post it before we go in."

"That's a splendid idea, Harry. I don't see how you think of
everything the way you do."

"I think it's because my father's always talking about how one
ought to think of all the things that can go wrong. He says