‘It is nothing,’ said Rose. ‘You are tired. You want to rest. We will leave you.’

She seemed a little dazed as we took our departure.

‘Well,’ said Rose when we were outside. ‘What do you think of it?’

He shot a sharp glance sideways at me.

‘I suppose her mind must be totally unhinged,’ I said slowly.

‘It struck you like that?’

‘No—as a matter of fact, she was—well, curiously convincing. When listening to her I had the impression that she actually had done what she claimed to do—worked a kind of gigantic miracle. Her belief that she did so seems genuine enough. That is why—’

‘That is why you say her mind must be unhinged. Quite so. But now approach the matter from another angle. Supposing that she did actually work that miracle—supposing that she did, personally, destroy a building and several hundred human beings.’

‘By the mere exercise of will?’ I said with a smile.

‘I should not put it quite like that. You will agree that one person could destroy a multitude by touching a switch which controlled a system of mines.’

‘Yes, but that is mechanical.’

‘True, that is mechanical, but it is, in essence, the harnessing and controlling of natural forces. The thunder-storm and the power house are, fundamentally, the same thing.’

‘Yes, but to control the thunderstorm we have to use mechanical means.’

Rose smiled.

‘I am going off at a tangent now. There is a substance called wintergreen. It occurs in nature in vegetable form. It can also be built up by man synthetically and chemically in the laboratory.’

‘Well?’

‘My point is that there are often two ways of arriving at the same result. Ours is, admittedly, the synthetic way. There might be another. The extraordinary results arrived at by Indian fakirs for instance, cannot be explained away in any easy fashion. The things we call supernatural are not necessarily supernatural at all. An electric flashlight would be supernatural to a savage. The supernatural is only the natural of which the laws are not yet understood.’

‘You mean?’ I asked, fascinated.

‘That I cannot entirely dismiss the possibility that a human being might be able to tap some vast destructive force and use it to further his or her ends. The means by which this was accomplished might seem to us supernatural—but would not be so in reality.’

I stared at him.

He laughed.

‘It’s a speculation, that’s all,’ he said lightly. ‘Tell me, did you notice a gesture she made when she mentioned the House of the Crystal?’

‘She put her hand to her forehead.’

‘Exactly. And traced a circle there. Very much as a Catholic makes the sign of the cross. Now, I will tell you something rather interesting, Mr Anstruther. The word crystal having occurred so often in my patient’s rambling, I tried an experiment. I borrowed a crystal from someone and produced it unexpectedly one day to test my patient’s reaction to it.’

‘Well?’

‘Well, the result was very curious and suggestive. Her whole body stiffened. She stared at it as though unable to believe her eyes. Then she slid to her knees in front of it, murmured a few words—and fainted.’