As they spoke, the tall lady proudly mounted the last step and came face to face with the Marquis of Marne. His lips moved, but something happened before he could speak.
A scream rang across the open space and went wailing away in echoes along those hollow walls. By the abruptness and agony with which it broke from the woman's lips it might have been a mere inarticulate cry. But it was an articulated word; and they all heard it with a horrible distinctness.
"Maurice!"
"What is it, dear?" cried Lady Outram, and began to run up the steps; for the other woman was swaying as if she might fall down the whole stone flight. Then she faced about and began to descend, all bowed and shrunken and shuddering. "Oh, my God," she was saying. "Oh, my God ... it isn't Jim at all ... it's Maurice!"
"I think, Lady Outram," said the priest gravely, "you had better go with your friend."
As they turned, a voice fell on them like a stone from the top of the stone stair, a voice that might have come out of an open grave. It was hoarse and unnatural, like the voices of men who are left alone with wild birds on desert islands. It was the voice of the Marquis of Marne, and it said: "Stop!"
"Father Brown," he said, "before your friends disperse I authorize you to tell them all I have told you. Whatever follows, I will hide from it no longer."
"You are right," said the priest, "and it shall be counted to you."
"Yes," said Father Brown quietly to the questioning company afterwards. "He has given me the right to speak; but I will not tell it as he told me, but as I found it out for myself. Well, I knew from the first that the blighting monkish influence was all nonsense out of novels. Our people might possibly, in certain cases, encourage a man to go regularly into a monastery, but certainly not to hang about in a mediæval castle. In the same way, they certainly wouldn't want him to dress up as a monk when he wasn't a monk. But it struck me that he might himself want to wear a monk's hood or even a mask. I had heard of him as a mourner, and then as a murderer; but already I had hazy suspicions that his reason for hiding might not only be concerned with what he was, but with who he was.
"Then came the general's vivid description of the duel; and the most vivid thing in it to me was the figure of Mr. Romaine in the background; it was vivid because it was in the background. Why did the general leave behind him on the sand a dead man, whose friend stood yards away from him like a stock or a stone? Then I heard something, a mere trifle, about a trick habit that Romaine has of standing quite still when he is waiting for something to happen; as he waited for the thunder to follow the lightning. Well, that automatic trick in this case betrayed everything. Hugo Romaine on that old occasion, also, was waiting for something."