Gunsmoke starts out in a strange place and time - Texas in 1858. The leader of an outlaw gang shoots a young recruit because it appears he is going to chicken out during the upcoming bank robbery. Career criminal York (Edgar Buchanan) remarks that this was unnecessary, and the leader tells him his opinion is not wanted.
The gang goes into nearby town and robs a bank, taking a customer there, a cowboy, hostage, saying that they will release him later. Back in camp, somebody tells York that the hostage says that he thinks he recognizes York's voice and that he once put him on the straight and narrow when they were working the same ranch. York says - yes - he remembers the guy. He was starting to go wild and that York set him straight and turned him away from a life of crime. In the meantime the head of the gang says he intends to kill the hostage, not let him go. York shoots the head of the gang dead and releases the hostage. Somebody asks York - Who was so important to you that you would take such a chance? York says the kid was named "Matt Dillon".
Seventeen years later, in Dodge City, Old York comes into town. He knows Matt is the marshal there, and he plans to trade on Dillon's feeling of debt to York for his life to give him a pass on some crimes. Dillon does come to his aid and defense a couple of times. When York graduates to bank robbery, Dillon can't bring himself to shoot him as he rides off with the bank's money. The whole town is talking about how Dillon could not bring himself to shoot a criminal because of a past association, and Matt is wracked with guilt and conflict over two things that largely rule his life - loyalty to friends and impartial enforcement of the law. How will this turn out? Watch and find out.
It's interesting that Dillon's life was saved in his youth by actually doing something stupid. It's a good idea that a hostage never say he knows or recognizes his captors, but in this case it worked out. Because one of the captors recognized him, and had a bond of affection for him, his life was spared. The director was smart to only show Matt from a distance and never show his face or let viewers hear his voice. It would have intruded on the reality of the situation.