Jim and Slim, a couple of workers at a chemical plant in the fictional New England town of Ravensback, decide to call it a day and head for the bar. Unfortunately, a large buildup of pressure leaks from one of the pipes that starts to form a yellow toxic cloud that drifts across the ground. Meanwhile, a school bus is taking children home. After dropping one child off, five children left on the bus: Paul MacKenize, Jenny Freemont, Ellen Chandler, Tommy Button, and Janet Shore. Suddenly the bus passes through the yellow cloud.