They had reached and were passing the tower flanking the wall in which was the mysterious window. The roof rose higher there, but a little way above and beyond them was to be seen a hazy brightness as rising from the skylight of a room below. The climb to the higher roof presented little difficulty, and as the two men reached it each felt a thrill of excitement at the thought that the solution of the mystery was now about to be theirs. What were they going to look down upon? Noiselessly now, with the utmost caution, they crept forwards on hands and knees, nearer to the light, nearer still, checking their impatience with the thought that a slip or the slightest noise might mean failure, and more, might cost them their reputations if not their lives.
Foot by foot they drew themselves towards the lighted roof, till at last they could make out how it was contrived. Above the level rose an iron frame about six inches high and perhaps ten feet square. As they reached the structure they found it crossed and recrossed by stout iron bars bolted to the frame, and beneath there was a skylight of opaque glass. So their curiosity was baffled, for, although a light shone from the room below, it was impossible to distinguish any object in it.
They held a whispered consultation.
“We are not going to be beaten like this,” Von Tressen said. “We must get a look down somehow.”
It was not so easy. The roof window had evidently been constructed to guard not only against admittance either way, but also against observation.
“The only thing to do is to examine it closely,” Galabin whispered. “We may find a peephole.”
Silently they crawled round the edge of the framework examining every pane they could reach. All to no purpose; the painted glass tantalizingly refused to reveal the secret it covered. When they had completed the circuit of the frame Galabin suggested that he, as the lighter man, should venture out on to the cross bars and try for better luck in the centre. This was not an easy task, especially as it had to be effected without noise.
“Take care how you come back,” Von Tressen warned him. “That will be the most difficult part.”
Very slowly Galabin crawled out, snake-wise, upon the bars, gently feeling, as he went, the glass below each interstice. The Lieutenant watched him anxiously, rather chafing at his own inaction. Presently his attention was quickened as he became aware that Galabin was resting longer than usual over a certain square. Then as he anxiously watched, he saw his companion raise his arm and motion him to join him, but from the side running at right angles, no doubt to distribute the strain on the bars. Von Tressen at once began to crawl round and so towards his companion, his eagerness being restrained only by the warning hand which was still uplifted. It did not take long, however, to bring their heads close together, and Von Tressen could see that Galabin’s search had been rewarded.
Almost in the centre of the skylight a pane of glass was defective. It moved slightly in its leaden casing, and one corner had either been left clear through carelessness, or a scrap of the colouring with which it had been covered had by some means been removed. Anyhow there was left practically a peephole through which nearly the whole of the room beneath was clearly visible. Galabin raised his head, and signed to Von Tressen to look down.