Shaw takes his oath he didn't see him.

I'll lay any odds they will beat those coverts to-night, and, by George! we'll nail some of them, if we have an ounce of luck." Ralph's sporting instinct, to which even the fleeting vision of a chance weasel never appealed in vain, was now thoroughly aroused, and even Charles shared somewhat in his excitement.
How could he warn Raymond to lie close?
The more he thought of it the more impossible it seemed.

It was already late in the afternoon.

He could not, for Raymond's sake, risk being seen hanging about in the woods near Arleigh for no apparent reason, and Raymond was not expecting to see him in any case for two days to come, and would probably be impossible to find.

He could do nothing but wait till the evening came, when he might have some opportunity, if the night were only dark enough, of helping or warning him.
The night was dark enough when it came; but it was unreliable.