Survivors'plane crashed in the middle of the way. They crashed into a desert. But it wasn't a desert. It was just a desert after the city was deserted. They accidentally entered a mysterious building. They went into a research center in ceda. They caught some uninfected people. People accept their test (surviving in a maze made by ceda, but some zombies evolved and the Institute was abandoned). Survivors have to go into the Institute to collect evidence and return to the maze to find a way out...