Dean helps Jenna, the nurse he met after the Darkness fell, get back home safely and then sets off to help Sam deal with a town infected by a mysterious and deadly gas. However, when Jenna falls into dangerous hands, she calls Dean for help and Sam tells him to go back to her. Unfortunately for Sam, he isn't able to handle the townspeople turned monsters as easily as he thought. Raised by their dad to fight supernatural forces, grown siblings Dean and Sam crisscross the country in their 1967 Chevy Impala, investigating paranormal activity and picking fights with deadly demons, ghosts and monsters.