With the law on his trail, one of which would soon be the famous Rough Rider W. Henry Harrison Llewellyn, Doc found it impossible to find honest work. He soon turned to what he knew best, stealing horses. He formed a gang called the Ponyboys and reportedly stole over 2,000 head of horses from ranchers and Sioux over a two-year period. His success along with his notoriety soon christened the Nebraska Territory “Doc Middleton Country.” Most people who knew him spoke kindly, saying that he had Robin Hood-like discretion when “hoss-thieving.”
Llewellyn soon grew tired of the chase and offered Doc a fake pardon planning to assassinate him out on the prairie. Doc learned of the plan and was injured in a ferocious gun battle that left him wounded and soon imprisoned. While in prison the rest of the Ponyboys were hunted down and hung, most without trial. In 1893, he rode in the great Chadron - Chicago horse race with ‘Buffalo’ Bill Cody. At the end of his life, a white moustache replaced Doc’s long, wavy beard. By this time he came to make his living running tent saloons in railroad boomtowns and remembering a time when the west was free.