Watch Out for a Small Man, by H. Bedford-Jones (epub/Kindle/pdf)

Mitchell had not the slightest intention of getting involved in any fracas when he went aboard the Tropic Bird at St. Louis, but this did not prevent him taking precautions as usual. He knew the Missouri. He was St. Louis agent for a dozen mercantile firms. He was going upstream this trip to deliver twenty thousand dollars in cash to Josiah Clegg of the Western Land Company at Council Bluffs, and for no other purpose. The last thing he wanted or expected was to get mixed up in anyone else’s war.