California girl Susan Murphy's wedding day is spoiled when a goo-filled meteorite lands on her, making her mutate. She grows to almost 50 feet tall!
Thinking she's a monster (well, she is now!), the military quickly capture her. They bung her in a high security prison along with a bunch of monsters, including a mutant cockroach, an ape-fish-wotsit, and a slithery blob. They've been there since Ye Olde 1950s, all pretty much forgotten.