Doomwatch (1970)
I can't even give the title of this episode in case it spoils anyone's future viewing.
Sadly the final two episodes of the first series were wiped and never recovered by the BBC so the events of this episode, the opening one of series 2, came as a bit of a shock.
Just as shocking is the sub plot in which Professor Ridge goes investigating genetic experiments. What he finds is well, just wow!!! I never thought 70's tv would be as cutting edge as it's become.
After a shaky opening couple of episodes,
Doomwatch is fast becoming a real favourite of mine.