The Undoing of Arlo Knott, by Heather Child, is unlike anything I’ve read before. It’s a book that grows in its power: it starts off like a single recorder being played out of tune but quickly builds up to a crashing crescendo with a show-stopping finale.

After a traumatic childhood incident, Arlo Knott discovers he can rewind time. He can undo any mistake, make uncanny predictions, impress friends and strangers, and chat up girls. But this temptation to undo and erase his mistakes isn’t the gift he initially thinks it is.

Sounds like fantasy, right? Click your fingers and go back in time – correct all the bad things that happen and stop awful things from happening in the future. But it doesn’t feel like fantasy. Child includes an impressive level of physics – through Arlo’s sister Erin and her girlfriend Nina – and the science behind Arlo’s gift is eventually unwound. You learn a lot about psychology too.

There’s romance: Arlo’s love is the driver behind much of the plot. And there’s action in the form of landmine detection, foreign hostage negotiation and life as a copper. Arlo Knott packs a lot in, yet it doesn’t feel contrived or hard to follow. Just like Arlo’s heavily edited, perfect life, this book makes no mistakes.

The plot sounds a little crazy, and the amount you go through with Arlo gave me a serious book hangover. But Child has tight control over this and never once slips up. Every action, every move, every relationship makes perfect sense.

Child’s main gift is character building. I hated Arlo to start with. Like, I really did not like the kid. But I couldn’t help myself from investing in him and his story. It takes a gifted writer and storyteller to create such a character while making you want more.

The way Child develops Arlo’s character is genius. He remains flawed, yet he shows real growth. Not just in his attitude to his gift, but in how he treats people. He starts thinking about the consequences and effects on others, and whether he has done more good or more bad.

We all say that hindsight is wonderful – but what if you could act on it? This is less Bernard’s Watch – and more like Black Mirror, with a healthy dose of The Butterfly Effect too. The twist in Arlo Knott took my breath away. I’m sure I strained my eyes finishing it: once you get to that point, there’s no going back.

I won’t give away the ending. But I will give you my thought process as I read (and re-read, and re-read, and re-read) the last three pages:

“Ah, got it. Right. Poor Arlo. Err. What? Hang on – HANG ON. REALLY? Is this –? Did that –? Oh my. Oh.”

The Undoing of Arlo Knott is a masterpiece. It ticks all of my boxes: fallible, human characters; an unpredictable plot; vivid descriptions and an effortless writing style; and thought-provoking scenes and issues. I finished it almost a week ago, but the moral and ethical dilemmas it raises still linger in my mind. I’m almost tempted to dock it a star for the serious book hangover it’s given me, but no…

5*

Thanks to NetGalley, Little, Brown Book Group (UK) and Heather Child for a copy of this ARC, in exchange for an honest and open review.