. . . . small towns on the frontier have little or no law at all.
There's no court to convince, no judge or jury to argue with to
prove
one's innocence. What there are are mobs that form spontaneously, convinced (as mobs will become) of what is obvoius -- even when it isn't so.
In the land where survival of the fittest is the law, Buck must find the highwayman -- and save himself from the hangman.