Days Gone opens with a forest encampment, and a man detailing how the world ended, how technology shut down, and how people began to lose their trust in others. Imagery shows barely any remnants of society and he goes on to say he remembers how it all began. He goes on to remember his girlfriend before this all happened. He goes on to talk about his life now, how he's a bounty hunter in this post-apocalyptic world.
In a quote from the PlayStation Blog-
"Set in the beautiful, volcanic scarred high-desert of the Pacific Northwest, Days Gone is an open-world action-adventure game where you play as Deacon St. John, a Drifter and bounty hunter who would rather risk the dangers of the broken road than live in one of the “safe” wilderness encampments."
A gameplay trailer of Days Gone was shown at the end of the conference. It shows the protagonist walking through an abandoned camp as he looks a car for some parts before continuing his search for his bounty. He runs towards a screaming man, when he finds him, a zombie-like child attacks the main character. It dies, and he and chases the bounty.
When he makes his way to the roof, he sees the area is swarmed with zombies, and he leaves his bounty to escape with his life. Doing everything he can to escape the inexplicable mass of zombies, he continues to navigate a building, shooting them when he can, and collapses a bridge that they run on. After shooting all the zombies he can, he welcomes the challenge of all the zombies that are flooding the area.