The instant afterward I saw Stanwick leap over the rivulet and take to flight.

That action roused me.

Without stopping for a word of explanation, I pursued him.
Unhappily, I missed my footing in the obscure light, and fell on the open ground beyond the stream.

When I had gained my feet once more, Stanwick had disappeared among the trees which marked the boundary of the park beyond me.

I could see nothing of him, and I could hear nothing of him, when I came out on the high-road.