Doc Adams is dispensing some free medical advice to Chester in one of the humorous heart to hearts the two often had when he recognizes one of three cowboys as Clem Maddow, somebody he knew years ago. Doc then says he is going to kill the man. He retrieves his Colt 36 from a file cabinet and clumsily loads it and heads out. Chester gets Matt who reasons with Doc and prevents him from shooting Clem.
But later that night a shot rings out and Clem is found in the street with a bullet in his back. Not only is Doc a suspect, he is the only physician in town and must tend to the gunshot wound of the man he wanted to kill. Meanwhile, Matt must figure out if it was somebody else trading on the known feud between Clem and Doc who shot Clem. If not, Matt may have just left a wounded man alone with a person who has tried to kill him.
Only at the very end does what happened between Clem and Doc come out. I'll let you watch and find out, but it might explain why Doc is a lifelong bachelor and why he became a doctor in the first place. You'll have to wait fourteen more years to find out Doc's actual first name though, but I will tell you it is not Cosmo.