“It looks to me as if they were flashing toward the north and a little toward the west,” said Dick, puzzled.

“That’s the way it seems to me, too,” agreed Harry.  “That isn’t what we expected, either, is it?”

“Of course we can’t be sure.”

“No, put it certainly looks that way.  Well, we can’t make sure from here, but we’ve got to do it somehow.  I tell you what.  We’ll circle around and get northwest of the house.  Then we ought to be able to tell a good deal better.  And if we get far enough around, I don’t believe they’ll see us, or pay any attention to us if they do.”

So they mounted their machines again, and in a few moments were speeding toward a new and better spot from which to spy on the house.  But this, when they reached it, only confirmed their first guess.  The signals were much more plainly visible here, and it was obvious now, as it had not been before, that the screen they had noticed had been erected as much to concentrate the flashes and make them more easily visible to a receiving station as to conceal the operator.  So they turned and figured a straight line as well as they could from the spot where the flashes were made.  Harry had a map with him, and on this he marked, as well as he could, the location of the house.  Then he drew a line from it to the northwest.

“The next station must be on this line somewhere,” he said.  “We’ll stick to it.  There’s a road, you see, that we can follow that’s almost straight.  And as soon as we come to a high building we ought to be able to see both flashes —­ the ones that are being sent from that house and the answering signals.  Do you see?”

“Yes, that’ll be fine!” said Dick.  “Come on!”

“Not so fast!” said a harsh voice behind them.

They spun around, and there, grinning a little, but looking highly determined and dangerous, was the same man they had seen the day before, and who had questioned them when the tire of their taxicab blew out!  But now he was not in uniform, but in a plain suit of clothes.

“So you are spying on my house, are you?” he said.  “And you lied to me yesterday!  No troops were sent to Croydon at all!”

“Well, you hadn’t any business to ask us!” said Dick, pluckily.  “If you hadn’t asked us any questions, we’d have told you no lies.”

“I think perhaps you know too much,” said the spy, nodding his head, “You had better come with me.  We will look after you in this house that interests you so greatly.”

He made a movement forward.  His hand dropped on Dick’s shoulder.  But as it did so Harry’s feet left the ground.  He aimed for the spy’s legs, just below the knee, and brought him to the ground with a beautiful diving tackle — the sort he had learned in his American football days.  It was the one attack of all others that the spy did not anticipate, if, indeed, he looked for any resistance at all.  He wasn’t a football player, so he didn’t know how to let his body give and strike the ground limply.  The result was that his head struck a piece of hard ground with abnormal violence, and he lay prone and very still.