As indicated on the back of the book:
This is the primary rulebook for Our Last Best Hope, a single session tabletop roleplaying game for three 3-5 players that takes about 2-3 hours to play. Our Last Best Hope is a game about a crew of people on a mission to save Humanity from a terrible Crisis. During the game, participants will play through a classic disaster movie, like Sunshine, Deep Impact, The Core, or Armageddon, where their characters are the stars. Each game is unique, comprising a new Crisis with a new set of characters and a new plan to save the Earth.
Example story lines from a session of Our Last Best Hope include:
...launching into space to stop a meteor from destroying all life on Earth.
...drilling to the center of the Earth to restart its molten core.
...navigating zombie filled cities to stop a nuclear holocaust.
Regardless of the Crisis, the characters played by the participants represent the last best hope for averting disaster.
Our Last Best Hope does not require a GM, nor is there any preptime required before the game starts. The game has is inspired by roleplaying classics like Fiasco and Polaris.