One peculiar day, Ava wakes up to find her parents and little sister gone. She tries calling them and that fails.
so she goes to her neighbor's house and sees that they are gone. After a few hours, she realizes that everyone is gone.

(She even tried calling 911, but nobody picked up)

So now she is alone. And it's her mission to find out where everyone went.

But there are some people that are still there, but she doesn't know about them.