A heartfelt and unexpected novel about an inseparable brother and sister, from the beloved author of Posted.

From the first moment Morgan can remember, Claire has always been there. Big sister and little brother. Cat and Mouse. They've always understood each other, saved each other, seen each other. And they stuck to their own code, unwritten but understood, that siblings were inseparable, that they had each other's backs, no matter what.

At least, they used to.

Somewhere along the line, things between them shifted. Claire started fighting more with Mom, storming out of the house, spending more and more time away, and Morgan felt his sister and best friend slipping away. Now he spends nearly every night sitting awake in his room, waiting for the sound of her key in the lock. It's a sound he hasn't heard in nearly a week, ever since her and Mom's worst fight ever. So when Claire finally calls and tells Morgan she wants to spend the day together, just the two of them, he knows this might be his only chance--not just to convince her to come home but to remind her how good things used to be and could be again.

But Claire has her own plan for the day. One that will mean that, no matter what happens, things between them are going to change forever.