Rejoining Warrender, Armstrong informed him of the discovery, and suggested that he should examine the contrivance for himself.
"I'll take your word for it," said Warrender, smiling. "I don't care about steeple-jack feats in half darkness. We'll wait a little before we follow that fellow through the tunnel. Let's go up and watch for the signal."
It was perhaps half an hour later when the light appeared above the tree-tops.
"Most certainly it's S.O.S.," said Armstrong, after counting the recurring glows.
"I shouldn't wonder if Pratt is right after all, and it's Molly Rod signalling. He was right about the organ pipe."
"Doesn't it occur to you that the light may come from the tower?"
"But if the forgers are at work there, why should any one signal?"
"Can't we discover whether it's from the tower or the house?"
"We can't take any bearings in the dark. Stay, though. If we move back from the window, and go to the side of the room, perhaps we'll find a spot where the light just becomes invisible. I'll mark that on the floor, and in daylight there'd be no difficulty."
Acting on this suggestion, they were not long in discovering the required spot. Warrender scratched a pencil mark on the floor; then they descended to the cellar, cautiously lifted the flagstone, and groped their way through the tunnel until they came to the chamber at the end. Nothing was altered there, except that the opened bale of paper had been removed. They had intended to enter the archway on the farther side, and lift the flagstone which, they suspected, closed the entrance to another cellar; but from above there came dully a succession of regular thuds which proved that somebody was about, and active.