Upstream or downstream?
Heaven alone knew! Whichever way he elected to go would be the wrong way.

Fate, who had saddled him with Silas and the mule, would see to that.
Then, having resentfully put his mind to it, he evolved some logic.
Brian, leaving the wood by the river, would not go back the way he had come.

He would travel upstream and mail his letter when he found the village.

Kenny conversely had found the village first.

Therefore he must travel downstream to find the wood; downstream through a disheartening tangle of bush and tree and brier and maybe snakes and marshes.
With a groan he plunged into the wood, keeping well up the slope to avoid the lower marshes.