Surviving a nuclear attack in the 1950s, the McCleans wake to find that the explosions have somehow propelled them into a post-apocalyptic United States that has been moved entirely underground. While the McCleans find a country caught in a never-ending war, they also learn that this new underground society might be willing to go to extreme lengths in order to destroy their enemies. Can the McCleans find a way to return to their own time before it's too late?