Going to spoil this movie, it’s been out for 60 years, so if you haven’t seen it yet and don’t want to be spoiled, stop here.
The “monster” is an atomic powered snail that gets all angsty, gets killed by a sailor, then it’s kids go on a killing rampage in one small town. There’s more than one of them and they never leave that one zip code, so the title of the movie is a completely lie.
If you can get past such a brutal truth, you’ll find this to be a fun creature feature with some fun set pieces.