At length, abruptly, I caught up with him, and found that we stood at the edge of the shallow pond Colonel Wragge had mentioned in his account the night before. It was long and narrow, filled with dark brown water, in which the trees were dimly reflected. Not a ripple stirred its surface.

“Watch!” he cried out, as I came up. “It’s going to cross. It’s bound to betray itself. The water is its natural enemy, and we shall see the direction.”

And, even as he spoke, a thin line like the track of a water-spider, shot swiftly across the shiny surface; there was a ghost of steam in the air above; and immediately I became aware of an odour of burning.

Dr. Silence turned and shot a glance at me that made me think of lightning. I began to shake all over.

“Quick!” he cried with excitement, “to the trail again! We must run around. It’s going to the house!”