The first in the series, Fallout is an open-world turn-based role-playing video game. The game has a post-apocalyptic and retro-futuristic setting, reminiscent of post-World War II United States and the fear that the country was headed for nuclear war.
Just before the bombs fell, some lucky people managed to reach safety of the Vaults, huge underground dwellings, during the war. Recently, the water purification controller chip in Vault 13 broke. Without clean water, the people of the Vault cannot survive. The protagonist is sent to find a replacement chip and ventures outside to face a dangerous world, hoping to return within a hundred and fifty days before the water runs out.