The world- every world- has ended, at least that's what the letter claims. Nobody has any way of knowing if this is true or not.
All they know is that one minute they were going about their lives, and the next they are in an office of the Empire State Building in New York with a letter in their hand instructing them to join "the network" and telling them to please feel free to contact the letter's author if they have any questions or requests.
Now they're stuck in an empty replica of Earth, with everything they could want provided for them. But can this really be called life?