The titular Martin Kane, P. I. is played by William Gargan. I mention that because the role went to a variety of actors over the five years of its run.
The retrial of a man previously convicted of robbing a grocery store and killing the wife of the owner is in progress when a surprise witness appears and says that he committed the robbery and the murder, not the accused. The catch is that the surprise witness is under sentence of death for a gangland killing, scheduled for execution in two weeks. When the D. A. steps forward to cross examine him, the witness pulls out a gun and kills the D. A. The witness then says that the defense attorney slipped him the gun and that, being condemned to death, there is nothing that can be done to him. The defense attorney denies any involvement and Martin Kane is on the case.
This one turned out to be rather involved to the point that, when the responsible parties are revealed, I went - WHO?? - and had to play back earlier portions of the episode to see just who it was being talked about. I can just imagine how confused the people gathered around their flickering cathode ray tubes would have been in 1951 with no means to rewind anything.
Humorous stuff I noticed - so many close-ups so that there is no need for fancy art design and the sets can be dressed cheaply. Also, William Garghan as Kane is always wearing that trench coat. I wonder if he wears it to the beach?
The one set that the producers did bother to dress - The one in the tobacco shop where, for some reason, all of the principal players gather to discuss clues and plot developments. Of course it is because the show's sponsor is a tobacco company! The police are sure to save on pensions by encouraging all of that smoking in their ranks!