She laughed a quick, fluttering laugh as she raised her head candidly to face him. "You remember the old dead tree at the top of the slope," she said, "when I found myself growing suddenly tired? I was tired, but I could have gone on a little farther—only I wanted to stop there."
"It was a gaunt old shell of a tree—hollow—" Dexter stopped to stare at her. "I know now!" he exclaimed. "It was one of Stark's stations. There's a telephone in the trunk of that tree."
Alison nodded. "As I told you before, I figured my brother'd spend the night at this cabin. And not knowing you were so close behind him, there was a danger of his oversleeping and being there next morning when you arrived. I thought I could warn him by telephone. I started to ring the cabin that night while you were gathering sticks for the fire, but you came back too soon for me. I had the receiver off, but didn't dare finish the call. You didn't give me another chance. But I must get word to Archie. So that night when you were asleep I slipped away to come here, intending to return to your camp before daylight.
"When I reached here," she pursued, "there was no Archie. You know what did happen—how I was forced to barricade myself in the cabin. In my fright I remembered the phone in the old hollow tree. The receiver was down and you had spread your blankets against the trunk. It was my only hope—to make you hear—and I screamed into the transmitter at this end, calling your help."
He looked at her soberly for an instant, and then laughed under his breath. "As simple as that! It was like a ghost voice whispering to me from the darkness, small and unreal, yet your voice."
"And knowing no more than that," she said softly, "you came."
He did not answer, but had turned with an absent-minded air, as though for no particular reason his attention was caught again by the hole in the chimney where the telephone instrument had been secreted. For a moment he stood silent, with thoughtfully puckered brows, and then, with a quick movement, he faced about once more to look at Alison.
"In the three cabins I have visited," he asserted, "the bunks were built like this one, placed against the side of the fireplace. Were the phones all concealed in the chimneys by the bunks, like this one?"
"Yes," she replied.
He nodded, and then as though he had forgotten her presence, he strode to the open window to stare into the twilight, with a pensive, far-off look in his eyes. But after a minute or two he turned to pace back across the floor, his head bowed abstractedly as he whistled a meaningless little tune between his teeth. Suddenly he halted before the girl. "I was thinking—" he began, and stopped.