Mr. Challoner had been honest in his statement regarding the departure of Sweetwater. He had not only paid and dismissed our young detective, but he had seen him take the train for New York. And Sweetwater had gone away in good faith, too, possibly with his convictions undisturbed, but acknowledging at last that he had reached the end of his resources. But the brain does not loose its hold upon its work as readily as the hand does. He was halfway to New York and had consciously bidden farewell to the whole subject, when he suddenly startled those about him by rising impetuously to his feet. He sat again immediately, but with a light in his small grey eye which Mr. Gryce would have understood and revelled in. The idea for which he had searched industriously for months had come at last, unbidden; thrown up from some remote recess of the mind which had seemingly closed upon the subject forever.

“I have it. I have it,” he murmured in ceaseless reiteration to himself. “I will go back to Mr. Challoner and let him decide if the idea is worth pursuing. Perhaps an experiment may be necessary. It was bitter cold that night; I wish it were icy weather now. But a chemist can help us out. Good God! if this should be the explanation of the mystery, alas for Orlando and alas for Oswald!”

But his sympathies did not deter him. He returned to Derby at once, and as soon as he dared, presented himself at the hotel and asked for Mr. Challoner.

He was amazed to find that gentleman already up and in a state of agitation that was very disquieting. But he brightened wonderfully at sight of his visitor, and drawing him inside the room, observed with trembling eagerness:

“I do not know why you have come back, but never was man more welcome. Mr. Brotherson has confessed.”

“Confessed!”

“Yes, he killed both women; my daughter and his neighbour, the washerwoman, with a—”

“Wait,” broke in Sweetwater, eagerly, “let me tell you.” And stooping, he whispered something in the other’s ear.

Mr. Challoner stared at him amazed, then slowly nodded his head.

“How came you to think—” he began; but Sweetwater in his great anxiety interrupted him with a quick:

“Explanations will keep, Mr. Challoner. What of the man himself? Where is he? That’s the important thing now.”

“He was in his room till early this morning writing letters, but he is not there now. The door is unlocked and I went in. From appearances I fear the worst. That is why your presence relieves me so. Where do you think he is?”

“In his hangar in the woods. Where else would he go to—”

“I have thought of that. Shall we start out alone or take witnesses with us?”

“We will go alone. Does Oswald anticipate—”

“He is sure. But he lacks strength to move. He lies on my bed in there. Doris and her father are with him.”

“We will not wait a minute. How the storm holds off. I hope it will hold off for another hour.”

Mr. Challoner made no reply. He had spoken because he felt compelled to speak, but it had not been easy for him, nor could any trifles move him now.

The town was up by this time and, though they chose the least frequented streets, they had to suffer from some encounters. It was a good half hour before they found themselves in the forest and in sight of the hangar. One look that way, and Sweetwater turned to see what the effect was upon Mr. Challoner.

A murmur of dismay greeted him. The oval of that great lid stood up against the forest background.

“He has escaped,” cried Mr. Challoner.

But Sweetwater, laying a finger on his lip, advanced and laid his ear against the door. Then he cast a quick look aloft. Nothing was to be seen there. The darkness of storm in the heavens but nothing more.—Yes! now, a flash of vivid and destructive lightning!

The two men drew back and their glances crossed.

“Let us return to the highroad,” whispered Sweetwater; “we can see nothing here.”

Mr. Challoner, trembling very much, wheeled slowly about.

“Wait,” enjoined Sweetwater. “First let me take a look inside.”

Running to the nearest tree, he quickly climbed it, worked himself along a protruding branch and looked down into the open hangar. It was now so dark that details escaped him, but one thing was certain. The air-ship was not there.

Descending, he drew Mr. Challoner hastily along. “He’s gone,” said he. “Let us reach the high ground as quickly as we can. I’m glad that Mr. Oswald Brotherson is not with us or—or Miss Doris.”

But this expression of satisfaction died on his lips. At the point where the forest road debouches into the highway, he had already caught a glimpse of their two figures. They were waiting for news, and the brother spoke up the instant he saw Sweetwater:

“Where is he? You’ve not found him or you wouldn’t be coming alone. He cannot have gone up. He cannot manage it without an assistant. We must seek him somewhere else; in the forest or in our house at home. Ah!” The lightning had forked again.

“He’s not in the forest and he’s not in your home,” returned Sweetwater. “He’s aloft; the air-ship is not in the shed. And he can go up alone now.” Then more slowly: “But he cannot come down.”

They strained their eyes in a maddening search of the heavens. But the darkness had so increased that they could be sure of nothing. Doris sank upon her knees.

Suddenly the lightning flashed again, this time so vividly and so near that the whole heaven burst into fiery illumination above them and the thunder, crashing almost simultaneously, seemed for a moment to rock the world and bow the heavens towards them. Then a silence; then Sweetwater’s whisper in Mr. Challoner’s ear:

“Take them away! I saw him; he was falling like a shot.”

Mr. Challoner threw out his arms, then steadied himself. Oswald was reeling; Oswald had seen too. But Doris was there. When the lightning flashed again, she was standing and Oswald was weeping on her bosom.