“Well, you see the hills beyond? They are really islands cut off on all sides by the impassable mire, which has crawled round them in the course of years. That is where the rare plants and the butterflies are, if you have the wit to reach them.”

“I shall try my luck some day.”

He looked at me with a surprised face. “For God’s sake put such an idea out of your mind,” said he. “Your blood would be upon my head. I assure you that there would not be the least chance of your coming back alive. It is only by remembering certain complex landmarks that I am able to do it.”

“Halloa!” I cried. “What is that?”

A long, low moan, indescribably sad, swept over the moor. It filled the whole air, and yet it was impossible to say whence it came. From a dull murmur it swelled into a deep roar, and then sank back into a melancholy, throbbing murmur once again. Stapleton looked at me with a curious expression in his face.

“Queer place, the moor!” said he.

“But what is it?”

“The peasants say it is the Hound of the Baskervilles calling for its prey. I’ve heard it once or twice before, but never quite so loud.”

I looked round, with a chill of fear in my heart, at the huge swelling plain, mottled with the green patches of rushes. Nothing stirred over the vast expanse save a pair of ravens, which croaked loudly from a tor behind us.

“You are an educated man. You don’t believe such nonsense as that?” said I. “What do you think is the cause of so strange a sound?”