This kind of thing - of a infection from radioactive contamination that causes irreversible mutation - absolutely terrified me. There is one scene where a man emerges from the mist with clawed hands and three-toed feet, weeping from hunger because "the stronger ones" won't share their hunts with him. He became an image of feverish nightmare for me. Meanwhile, the daughter keeps hearing someone call to her, perhaps her missing fiancee, a presence who comes ever closer to the house. Though she has fallen for the scientist, she feels somehow beholden to the mysterious creature, who when revealed is (admittedly rather campily) monstrous and invulnerable until the scientist realizes that it fears the uncontaminated.
This is really great fun and brought me back to my childhood terror of nuclear holocaust. Radiation was such a mysterious thing then. The acting is also unusually good for low budget scifi of the 50s, with Connors (or Minnix) as the thuggish tough, but also Denning, who was in many 60s TV shows. Just this film is well worth the price of the dvd. It is by far my favorite of the Corman legacy.
Recommended with enthusiasm.