He thought at first that it was a blurring of the glass by some stronger gust of rain, but the next moment his experience told him that it could not be so.

He had seen a shadow, and the shadow was that of a man, sliding along against the wall of the house, in order that he might not be seen by a sentinel.
Harry's suspicions were up and alive in an instant.

In this border country spies were numerous.

It was easy to be a spy where people looked alike and spoke the same language with the same accent.

His suspicions, too, centered at once upon Shepard, whom he knew to be so daring and skillful.
The lad was prompt to act.