In a vast underground bunker in Colorado set three years post-apocalyptic global disaster, the series chronicles Secret Service agent Xavier Collins (Sterling K. Brown) as he tries to solve the murder of U.S President Cal Bradford (James Marsden) in three years. Collins gets further in the investigation only to discover a labyrinth of conspiracies among the elite residents of said bunker, especially its founder and most cunning billionaire Samantha “Sinatra” Redmond (Julianne Nicholson). The threads of present-day investigation and flashbacks come together to reveal the backstory behind how humanity got to the apocalypse and the web of relationships.