Philip Stewart is in prison for a year for manslaughter because a man he punched in a disagreement later had a fatal coronary attributed to stress from the fight. Shortly before his release he begins to refuse to see his wife, whom he married shortly before the fatal altercation. He gives no reason for his refusal.
At the same time, a sleezy independent insurance investigator, Jack Mallory, is sniffing around both Stewart and his wife because a very expensive diamond went missing at the time of Stewart's arrest and lots of people think that he had something to do with it.
In spite of the fatal fight Stewart had at the company, in spite of the missing diamond, Stewart is given his old job back. At some point, Mallory shows up at Stewart's place of employment and yet another fight breaks out. In the process Stewart punches Mallory in the nose, and shortly thereafter Mallory is found in the elevator, dead of a gunshot wound. Nothing accidental here this time, plus it can be proved that nobody was in the elevator except Mallory and Stewart from the time they entered the elevator until Mallory's body was discovered. Again, Stewart is arrested but pleads his innocence and Perry Mason is on the case.
Besides the normal situation of people causing trouble for themselves and Perry by not getting disagreements and suspicions out in the open, in the words of Cher in Clueless - "This place is a lawsuit waiting to happen!" The jewelry company 's secretary is being habitually harassed by a worm of an employee who gives worms a bad name, there is no organized means of keeping track of the company's expensive inventory of jewels, and a guy convicted of killing a fellow employee gets his old job back after serving his sentence AND is allowed to keep a gun in his desk drawer!
This is really a pretty tame episode of Mason - Not particularly bad or good, with no super clever tricks up the writers' or Perry's sleeves. Still, average Mason is still superlative TV.