It was not his place to reckon on the possible achievements of others.

So far as this errand was concerned, and so far as he was now concerned, there was nobody in the world but himself.

Swiftly he reckoned the chances.
He changed the pace of his horse into an easy gallop and sped along the road.

But the horse did not have sufficient reserve of strength to increase his speed and maintain the increase.

He knew without looking back that the Union riders were gaining, and he continued to mature his plan.
Harry was now cool and deliberate.