With most of it based on a truck stop called Gil's Pitstop on a Georgia highway, "400 Days" tells five linked stories; each taking place at different points in time and from the point of view of a different survivor, from one day before the undead apocalypse to day 400.
The five stories can be played in any order and will change based on the choices that you make. Echoes of the choices you made in Season 1 will carry over into "400 Days" and the choices you make in "400 Days" will resonate into Season 2.
At the end of "400 Days", the stories are wrapped up, and leaves a few hints towards what we can anticipate to see from Season 2.