Daniel recognises shards of himself in the boy: the sudden anger and fear; the dysfunctional background which in his case meant carrying a flick-knife, being erratically raised in a series of foster homes, becoming a runner - often from his girlfriends. He's a success on the surface; a mess underneath.
As events shuttle between London and a scruffy farmhouse in Cumbria, evidence against Sebastian builds.
There are witnesses and bloodstains, testimonies from parents about his terrorising other children with broken glass.
By halfway through, we're into a series of high-drama trial scenes, which lead to a shocking (if predictable) verdict, and then an equally shocking (and equally predictable) revelation.
Oh, and a romance.
Ballantyne builds a big, boldly drawn cast of characters: Minnie the gin-swigging proxy mother; the jungle of schoolkids; the father who manifests "a seismic arrogance and wealth"; the twangy wife in her apartment of Chinese vases.
Is it the "Phenomenon" the blurb claims? Maybe - until the next one comes along. No, I'm not scoffing; there's a raw force in its best parts, an appalled incredulity that keeps it charging forward.
But the structure is mechanical, and the style frequently falters. It's adjectival, sometimes awkwardly formal, intermittently clumsy. Ballantyne's next book should be one to anticipate, but let's hope it comes with more editorial discipline and fewer publisher's ecstasies.