This four part episode of PBS's Mystery was one of several films patterned loosely after the Doctor Crippen case of 1910. Dr. Crippen was not really an M. D. at all, and instead was a doctor of homeopathy who hawked patent medicines. He was convicted of killing his wife Cora in 1910. The only direct evidence against him - a "mass of torso flesh" buried in his basement, found after his wife disappeared and he panicked and ran as a result of the ensuing police investigation. His motive - wanting to marry his mistress. In 2007 DNA analysis showed that the "mass of torso flesh" was not Cora Crippen and was not even female. So Dr. Crippen more than likely did something wrong and maybe even killed his wife, but the body parts found in his basement upon which his conviction was based did not belong to her.
In 1979, when this was produced, there was no such knowledge. Everyone assumed the body found was that of Crippen's wife. In this extremely loose adaptation of the Crippen case, Dr. Edmund Bickleigh is an actual doctor with a general practitioner's practice in a rural place in England. He lives well but by no means is he rich. He and his wife Julia are strangers living under the same roof, but that's OK because the good doctor "gets around". And to be such a mousey looking fellow - but not mousey acting - he gets some very good-looking girlfriends. But one in particular, the beautiful and cultured Madeleine, has him wanting to marry her. Julia is first receptive to the idea of a divorce until she meets Madeleine and then says that the woman is just a flirt and a tease, and she will not divorce him since this woman could only bring him unhappiness.
At that point, Bickleigh decides Julia must die. That's not just because she is refusing the divorce, but because Madeleine says that her religion would not allow her to marry a divorced man. So Bickleigh alternately poisons his wife's grapefruit with a substance that gives her terribly painful headaches and then gives her morphine to kill the pain. He turns her into an addict, makes sure this is common knowledge , and then delivers the final deadly dose himself with a carefully scripted alibi. Nobody suspects murder as everyone believes that Julia delivered the final and fatal overdose herself. But Bickleigh has left a few loose ends around, plus he has made a couple of enemies who are suspicious of him. So complications ensue including a couple of unsuccessful murder attempts to cover up the original murder of his wife.
This was a very well done production, and for sure Dr. Bickleigh is a more deliberate character than Dr. Crippen ever was, as his character never panics the way Crippen did. It does look like the director changed strategies from episode to episode, though. In the first episode the score plays repetitively to the point of being annoying. It is completely gone in the subsequent episodes. Then there is a narrator saying what Bickleigh is trying to do. In the final episode, the narrator is gone and instead the audience hears the doctor's thoughts.