According to Hoyle

By the close of 1882 in the American West, the line between heroes and villains is narrow. Total chaos is staved off only by the few who take the law at its word and risk their lives to uphold it. But in the West, the rules aren't always played according to Hoyle. US Marshals Eli Flynn and William Henry Washington-longtime friends and colleagues-are escorting two prisoners to New Orleans for trial when they discover there's more than outlawry to the infamous shootist Dusty Rose and the enigmatic man known as Cage.
As the two prisoners form an unlikely partnership, the marshals can't help but look closer at their own. When forces beyond the marshals' control converge on the paddle wheeler they've hired to take them downriver, they must choose between two dangers: playing by the rules at any cost, or trusting the very men they are meant to bring to justice.(This title is a revised and edited second edition, with minor new additions, of According to Hoyle, originally published elsewhere.)