At thirty-five, Federal Marshal Buck Fyffe has had eleven years' experience as a lawman. When he and Deputy Steve Larson were charged with taking the outlaw Luther Gibbs to the newly established Yuma Territorial Prison, he wasn't expecting any problems. But when Larson gets snake bit and dies, Fyffe finds himself almost three days away from the Yuma prison with no one to spell him while he sleeps. Gibbs and his gang had stolen 25,000 dollars from Southwestern, but only Gibbs knew where it was hidden and he knew the gang would be looking for their leader. It doesn't take long for Gibbs's gang to find them. Fyffe is overtaken by the gang and suffers at their hands. The gang hatches a plan for Gibbs to pose as Fyffe and one of his men to pose as Larson. They deliver Fyffe to Yuma prison, claiming he is Luther Gibbs. In spite of Fyffe's insistence that he is in fact the federal marshal, he finds himself as prisoner number 109. Now, in addition to fearing that Gibbs will get to the money and get away, Fyffe must survive in a prison where he is sure that someone he has previously sent to prison will recognize him and exact their revenge.