Ride the Savage River. Large Print (en Inglés) - Scott Connor

It took Marshal Ellis Moore twelve years to clean up Empire Falls, and he was killed taking on the last of the gun-toters who had controlled his town. But at his funeral U.S. Marshal Lincoln Hawk told his sons Daniel and Henry that all was not as it seems. Ellis had been on the payroll of Samuel Holdstock, who controlled Skull Bend from his steamboat, and who was now spreading his corrupting influence downriver.
Daniel and Henry vowed to expose the full truth. To do that they would need to infiltrate Samuel's domain, spirit him away from his steamboat, and then deliver him to justice in Empire Falls. Even the formidable Lincoln Hawk reckoned their mission was doomed to fail, but to put right their father's mistakes they would have to succeed.