Escape from Fort Benton. Large Print (en Inglés) - Scott Connor

Nathan Palmer and Jeff Morgan happen across an ambush too late to help the victims, but a dying man gives them a gun, a key and a cryptic message about 10,000 dollars being available in Fort Benton in five days' time.
Now Nathan and Jeff set about getting their hands on the money. However, Fort Benton is the private empire of Mayor Decker and his ruthless form of justice. Before the day is out the pair are beaten up and thrown in jail.
In Decker's clutches, they're going to need all their courage if they are ever to escape.