They were rocking, lurching, twisting, swaying in their mad struggle—and now they circled more widely—and branches snatched and tore at them, and broke and fell from the trees at the sides of the path. And here Locke gave a step, and there another, working nearer and nearer to the edge of the lawn.

And then suddenly there came a half-choked cry from the other. The man had tripped in the undergrowth. Locke swung his weight to complete the fall—tripped himself—and both, with their balance gone, but grappling the fiercer at each other, pitched headlong with terrific force into the trees at the side of the path.

And Locke was for an instant conscious of a great blow, of streaks of fiery light that smote at his eyeballs with excruciating pain—and then utter blackness came.

When he opened his eyes again a moonbeam lay along the path, and a figure in a long dressing gown was passing by. He was dreaming, wasn't he? There was a sick sensation in his head, a giddiness—and besides that it gave him great pain. He raised himself up cautiously on his elbow, fighting to clear his mind—and suddenly his lips tightened grimly. There was something ironical in that moonbeam—something that mocked him in disclosing a figure in a dressing gown instead of a face that had been unmasked yet still could not be seen. He looked around him now. He was lying a few feet in from the edge of the path, and against the trunk of a large tree. Yes, he remembered now. His head had struck against the tree and he had been knocked unconscious. And the man who had been masked was gone.

He rose to his feet. He was very groggy—and for a moment he leaned against the tree trunk for support. The giddiness began to pass away. That was old Mr. Marlin who had just gone by. Well, neither the old madman nor his money had come to any harm, anyway! He stepped out on the path, and from there to the edge of the lawn. The old madman was just disappearing around the corner of the verandah.

Locke put his hands to his eyes. How his head throbbed! How long had he lain there unconscious? He took out his watch. His eyes seemed blurred—or was it the meagreness of the moonlight? He was not quite sure, but it seemed to be ten minutes after three. It wasn't very easy to figure backward. He did not know how long he and the old maniac had been together in the aquarium, but, say, half an hour. Starting then at the hour of the rendezvous, which had been at a quarter past two, that would bring it to a quarter of three; then, say, ten minutes for what had happened afterward, including the fight, and that would make it five minutes of three. He must therefore have been lying in there unconscious for at least fifteen minutes.

The man who had worn the mask was gone now—naturally. But perhaps it would not be so difficult to pick up the trail. Captain Francis Newcombe's room offered very promising possibilities—and there was a torn coat sleeve that would not readily be replaced in fifteen minutes!

He made his way now across the lawn, and up the steps to the verandah. He tried the front door. It was locked. Of course! He had forgotten that he had left the house by crawling out of the aquarium window. There was no use going back that way because the old madman had locked the aquarium door. Mr. Marlin, though, had some means of entrance—and if that door through which the man had so suddenly appeared in the back hall meant anything, the entrance the old man used was likely to be somewhere in the rear. But Mr. Marlin would probably have locked that, too, behind him.

He looked up and down the now moon-flecked verandah—and began to try the French windows that opened upon it from the front rooms of the house. The first two were locked as he had expected. It was only a chance, but he might as well begin here as anywhere else. He tried the third one almost perfunctorily. It opened at a touch.

"I'm in luck!" Locke muttered, and stepped inside.