I'd say this was the worst of the Karnsteins. The screenplay is disjointed, the theme is sledgehammered, the effects are shoddy, the Collinsons can't act, and when Cushing is obliged to start raving about discovering "twins of evil," it's a real humiliation for the grand old man. You can almost see him cringe, while some oaf is explaining from the sidellnes that this is the big chance for Pete to sell the title to the suckers out there. You just know this got made because some horndog Hammer exec saw the twins nude in Playboy and decided that they should be nude in a movie, too. Stunt cinema at its weakest.