I was still rather raw over the deception which had been practised upon me, but the warmth of Holmes’s praise drove my anger from my mind. I felt also in my heart that he was right in what he said and that it was really best for our purpose that I should not have known that he was upon the moor.

“That’s better,” said he, seeing the shadow rise from my face. “And now tell me the result of your visit to Mrs. Laura Lyons—it was not difficult for me to guess that it was to see her that you had gone, for I am already aware that she is the one person in Coombe Tracey who might be of service to us in the matter. In fact, if you had not gone today it is exceedingly probable that I should have gone tomorrow.”

The sun had set and dusk was settling over the moor. The air had turned chill and we withdrew into the hut for warmth. There, sitting together in the twilight, I told Holmes of my conversation with the lady. So interested was he that I had to repeat some of it twice before he was satisfied.

“This is most important,” said he when I had concluded. “It fills up a gap which I had been unable to bridge in this most complex affair. You are aware, perhaps, that a close intimacy exists between this lady and the man Stapleton?”

“I did not know of a close intimacy.”

“There can be no doubt about the matter. They meet, they write, there is a complete understanding between them. Now, this puts a very powerful weapon into our hands. If I could only use it to detach his wife—”

“His wife?”

“I am giving you some information now, in return for all that you have given me. The lady who has passed here as Miss Stapleton is in reality his wife.”

“Good heavens, Holmes! Are you sure of what you say? How could he have permitted Sir Henry to fall in love with her?”

“Sir Henry’s falling in love could do no harm to anyone except Sir Henry. He took particular care that Sir Henry did not make love to her, as you have yourself observed. I repeat that the lady is his wife and not his sister.”

“But why this elaborate deception?”

“Because he foresaw that she would be very much more useful to him in the character of a free woman.”

All my unspoken instincts, my vague suspicions, suddenly took shape and centred upon the naturalist. In that impassive colourless man, with his straw hat and his butterfly-net, I seemed to see something terrible—a creature of infinite patience and craft, with a smiling face and a murderous heart.

“It is he, then, who is our enemy—it is he who dogged us in London?”

“So I read the riddle.”

“And the warning—it must have come from her!”

“Exactly.”