In order to prevent mankind from benefitting from a scientist's new invention, aliens possess the bodies of human beings to discredit them.
All four of the Mexican movies that marked the end of Boris Karloff's career are quite awful, but there is some variety in the range of awfulness. For my money, I consider this the best of a bad lot; it's not as repugnant as THE FEAR CHAMBER, it's not as deadly dull as DANCE OF DEATH, and it is more coherent than SNAKE PEOPLE. Karloff actually has a major role in the proceedings as well, which means he gets a little more in the way of screen time, and given that he's easily the best actor on the lot, that's a good thing. Still, the story doesn't really make much sense; in particular, I can't quite figure out why the aliens would wish to possess a known serial killer when he's really more trouble than he's worth. The movie is technically ghastly; keep your eyes open for some of the most blatant actor substitiutions in the fight scenes, and marvel at the fact that the actor who dubbed in a line for Karloff at one point not only doesn't sound remotely like him, but doesn't even appear to be trying to do so. The movie does muster up a bit of life near the end, but most of the various elements (the aliens, the deformed assitant, and the serial killer) never mesh into a satisfying whole, and the incompetent editing and sometimes queasy special effects (especially during the murder sequences) don't help matters any. Mexican movie fans might want to keep their eyes open for Yerye Beirute, who has appeared in a few other Mexican horror movies such as THE VAMPIRE'S COFFIN; he has one of those faces you can't forget.