Girl in the Walls

She doesn't exist. She can't exist.
'Those who live in the walls must adjust, must twist themselves around in their home, stretching themselves until they're as thin as air. Not everyone can do what they can.
But soon enough, they can't help themselves. Signs of their presence remain in a house.
Eventually, every hidden thing is found.'
Elise knows every inch of the house. She knows which boards will creak. She knows where the gaps are in the walls. She knows which parts can take her in, hide her away. It's home, after all. The home her parents made for her. And home is where you stay, no matter what.
Eddie calls the same house his home. Eddie is almost a teenager now. He must no longer believe in the girl he sometimes sees from the corner of his eye. He needs her to disappear. But when his older brother senses her, too, they are faced with a question: how do they get rid of someone they aren't sure even exists?
And, if they cast her out, what other threats might they invite in?