I've been looking out for this since I read Downham's second book You Against Me. It is written in the same clear, distinctively British way. It is a story of a teenage girl with terminal leukaemia. Despite the morbid subject matter, it's honest and not overly sentimental which is what sets it apart.
I love this book. I don't cry much, but this had me in tears for thirty pages straight. I'd definitely recommend giving this novel a try.