He continued his search, following the revealing foot prints.

He went nearly all the way around the house and then lost them among heavy shrubbery.

He surmised that at this point the spy--he was sure that it was a spy and sure, too, that it was Shepard--had left the place, passing between the sentinels in the rainy dark.
He spoke to the sentinels, who knew him well, and they were quite confident that nobody had come within their lines.

But Harry, while keeping his own counsel, held another opinion and he was equally positive about it.

He was returning to the house, when he heard the tread of hoofs, and then a horseman spoke with the sentinels.