Other reviewers have mentioned the actual plot points of this episode. The part that really had me yelling at the TV was the completely outdated approach to how everyone treated the child, Colin.
He's well under 16, so under the age of consent for any medical procedure (which is the closest analogy to the experiments) and yet not even his supposed defender, Tom, ever says "He's a child. You can't do this." None of the other adult have ANY care for Colin, not even really Anne.
I'm old enough to remember this show when it was broadcast, though I didn't really remember much about it, so I'm familiar with the attitudes of the period but even so I was completely shocked by the treatment of this poor boy.
It's a fairly gripping bit of telly, though with some flaws (no one could have shouted "look out" at the end?) but a sad indictment of how children could be treated in the late 70s.