The movie takes place immediately after the events of the first film. The Carter family, who survived the gruesome encounter with the mutant family in the desert, are now being transported to their new home in California. However, their convoy is ambushed by a group of mutants, led by the terrifying Papa Jupiter. The family is forced to take shelter in an abandoned military base, where they soon discover that the mutants are not just random attackers but are, in fact, a result of a secret government experiment gone wrong.