It's Maisie's birthday and she can't wait to open her presents.

She's hoping for the things she needs to build her own nuclear reactor.

But she wakes to an empty house and outside the front door is nothing but a terrifying, all-consuming blackness.

Trapped in an ever-shifting reality, Maisie knows that she will have to use the laws of the universe and the love of her family to survive. And even that might not be enough.