Young Marty, along with her little brother and stepmother, is forced to accompany her father—an environmental specialist—to yet another site for an inspection. The site turns out to be a military base housing a storage facility for toxic chemicals. While Marty makes new friends and explores her unfamiliar surroundings, her father takes water samples and talks with a local doctor, who tells him that people have been coming to him with obsessive fears: they’re afraid to sleep, afraid of every shadow, and even afraid of themselves. The doctor suspects that this is due to the chemical waste stored at the base. Soon, Marty’s brother Andy is also overcome by these fears; that same night, he discovers that his family has been replaced: he sees his mother die, and in her place appears another woman who looks exactly like the deceased. However, no one believes the little boy…