“They’ve got two men, at least — maybe a lot more, doing that,” whispered Harry.  “We’ve got to find out just how often he passes that spot.  We want to know if the intervals are regular, too, so that we can calculate just when he’ll be there.”

Three times the man came and went, while they waited, timing him.  And Harry found that he passed the spot at which they had entered every fifteen minutes.  That was not exact for there was a variation of a minute or so, but it seemed pretty certain that he would pass between thirteen and seventeen minutes after the hour, and so on.

“So we’ll know when it’s safe to make a dash to get out,” said Harry.  “The first thing a general does, you know, is to secure his retreat.  He doesn’t expect to be beaten, but he wants to know what he can live to fight another day if he is.”

“We’ve got to retreat, haven’t we?” asked Dick.  “It wouldn’t do us any good to stay here.”

“That’s so.  But we’ve got to advance first.  Now to get near that house, and see what we can find Look out for those traps and things our friend warned us of.  It looks like just the place for them.  And keep to cover!”

They wormed their way forward, often crawling along.  Both knew a good deal about traps and how they are set, and their common sense enabled them to see the most likely places for them.  They kept to open ground, avoiding shrubbery and what looked like windfalls of branches.  Before they came into full view of the house they had about a quarter of a mile to go.  And it was an exciting journey.

They dared not speak to one another.  For all about, though at first they could see nothing, there was the sense of impending danger.  They felt that unseen eyes were watching, not for them, perhaps, but for anyone who might venture to intrude and pass the first line.  Both of the scouts felt that they were tilting against a mighty force, that the organization that would perfect, in time of peace.  Such a system of espionage in the heart of the country of a possible enemy, was of the most formidable sort.

They stopped, at last, at the edge of the clump of thick, old trees that seemed to surround the place.  Here they faced the open lawn, and Harry realized that to try to cross it was too risky.  They would gain nothing by being detected.  They could find out as much here by keeping their eyes and ears open, he thought, as by going forward, when they were almost sure to be detected.

“We’ll stay here,” he whispered to Dick, cautiously.  “Dick, look over there —­ to the left of the house.  You see where there’s a shadow by that central tower?  Well, to the left of that.  Do you see some wires dangling there?  I’m not sure.”

“I think there are,” whispered Dick, after a moment in which he peered through the darkness.  Dick had one unusual gift.  He had almost a savage’s ability to see in the dark, although in daylight his sight was by no means out of the ordinary.