Like Dirk Bogarde in the 1968 film, Morse unwittingly swallows a drink spiked with a powerful hallucigen, with the first hint of something amiss coming when a telephone rings in a slightly odd way.
Both the 1970 film and this "Endeavour" story feature a "Clean Up TV" campaign, and both feature a repressed spinster daughter working for the campaign whose job is to transcribe bad language from TV shows and who is required to repeat the bad language in a flat, unemotional voice.