Review by Red-Barracuda

Early Hammer film before they hit upon the idea that horror was the way of the future. This one is a sci-fi effort about two young scientific geniuses who invent a duplicating machine; they both are in love with the same girl but she is in love with just one of them, so the other lovesick boffin asks her if he could make a duplicate of her. That'll save the day and make everybody happy, right? Wrong! This love triangle plus duplicate is the four sided triangle of the title. I suppose the sci-fi is more of a maguffin that allows the story to explore human emotional elements. Its not a bad effort really.