This is an odd beast, to say the least, and very difficult to get a good handle on. Visiting American tourist Simon Wells (Carey) picks up the tarty Joan (Field), only to find out quickly it's a scam, as he is mugged by her brother, King (Reed) and his gang of teddy-boys. But Joan is sick of her life and, encountering Simon on his boat later, opts to sail off with him, much to King's disapproval. He and his crew chase after the pair, and they end up on cliffs, near a mysterious remote facility run by Bernard (Knox), a scientist who refuses to talk about his work, which appears to involve a group of nine children kept in isolation. While clambering on the cliffs, Simon, Joan and King all find themselves joining the children, who keep them hidden from Bernard and his soldiers, though there is no apparent way of escape. An uneasy alliance is formed, with the aim of somehow rescuing the captive children from Bernard's capture, and whatever he may have had planned for them.
This feels almost like two films spliced into one, and the first half is more concerned about the relationships of the various characters - even those that turn out to be of little relevance to proceedings when they unfold - and is pretty feeble viewing. Once everyone gets to the research center, things warm up considerably. The makers would have been better off condensing events until that point into about five minutes, and perhaps telling more about the society the kids have created in their isolation; they're rather more polite and well-spoken than The Lord of the Flies, shall we say. One thing I really did appreciate was the bleakness apparent here; normally, Hammer movies went for the triumph of good over evil, true love conquering all, etc. Not wanting to give too much away, let's just say that doesn't quite take place here. The results are just about unique - not only in the Hammer canon, also in the realm of sixties sci-fi as a whole - and merit a look, despite its turgid opening.