"Does the date, April the 23rd, 1915, suggest anything to you?"
The other man thought for a few moments, then shook his head.
"Of course the War was on at that time—that accounts for Marle being employed in manufacturing, or inventing, explosives——"
"But he need not have had anything to do with explosives at all," Hugh broke in excitedly. "It was on April the 23rd that the first German attack was made in which they used asphyxiating gas! Silas Marle may have been employed in evolving retaliatory counter-measures."
Ronnie Brewster received his chum's suggestion with a careless shrug.
"Interesting, but scarcely informative," was his comment. "I flatter myself I'm not particularly slow in the uptake, but I'm hanged if I can see any connection between a retired government chemist and that precious cloven-hoofed Terror of yours. Why not see what is in the safe?"
Hugh nodded and, selecting the likeliest-looking key on the ring, inserted it in the brass-rimmed keyhole. It fitted—it turned—the ponderous bolts slid back. Grasping the handle, Hugh gave it a half-turn and the heavy door swung open, and as it did so, a loud gasp of amazement escaped his lips.
Until that moment he had scarcely paused to consider what a safe of these dimensions might contain; for all he knew he might be confronted with the dead body of Marle in a repulsive state of decomposition. But the object which met his gaze was less gruesome, though not less surprizing.
The sole content of the safe was a long, bulky, sealed packet, in every respect the counterpart of the one given to him by Joan Endean!
14
A look of the blankest mystification spread over Hugh's features as his eyes fell on the duplicate sealed packet. For it was an exact duplicate, not only in its general size and bulk, but down to such details as the peculiar texture of the paper and the heraldic device which adorned the large red seal. Such a likeness could not possibly be accidental. Either the packet lying before him was the same one that had been stolen from him in the Valley of Rocks, or else this was the genuine packet which the decoy one—containing nothing but blank papers—had been intended to safeguard. In any case, the presence of the latter in Marle's safe formed a strange and unexpected link between him and the mysterious Joan Endean.
"What's wrong, old man?" Ronnie's voice, tinged with a note of amused surprize, brought Hugh's speculations to an abrupt end. "You've been staring at that letter as though you were expecting to see it vanish in a whiff of brimstone. I believe the greedy beggar is disappointed because the safe wasn't packed tight with wads of banknotes!"
"Scarcely that." Hugh forced a smile as he shook his head. "But that letter happens to be a perfect facsimile of"—he paused, suddenly calling to mind Joan's stipulation of secrecy; adding, a trifle lamely—"of—of another letter that I have seen."
"Nothing wonderful in that," was the other's careless rejoinder. "Most letters have a family likeness on the outside—it's what is inside them that makes all the difference between a tender missive of love and a curt intimation that a check by return mail will oblige."
Trenchard picked up the letter and balanced it thoughtfully in his hand as he read the superscription:
