Rites, By Sophie Coulombeau

'When I was 14, I did something terrible. At least, that's what some people tell me." So opens Sophie Coulombeau's debut novel, and moral prevarication will twist throughout it. The "terrible" act was two pairs of 14-year-olds deciding to lose their virginity. And then one girl crying rape.

Rites doesn't challenge that basic premise we agree on – "no" means "no" – but it does make clear just how unclear that can be, when genuine mistakes are compounded by circumstance. Accusations fly, as the four teenagers find themselves in a swirl of petty revenge, understandable jealousy, fear of recrimination ....

So, it's about rites of passage, but with the teens all Catholics, and a smarmy priest in the mix, there's also a religious context to Rites. Look again at that opening line: from the first, the novel is, on one level, a confession. It's 15 years later, and the characters are retelling their stories to an unspecified, silent interviewer.

But this gives rise to a chit-chatty vernacular, as if transcribed faithfully from interview tapes, which quickly becomes annoying. It's far too self-conscious: lines such as "You only, like, stole my boyfriend" or "He always had a, sort of, fear of doing wrong, you know" labour the point. You can see what Coulombeau's aiming for – and in a rape case, exactly what language you use, and how, could be crucial in establishing guilt, and that's certainly the case here. But there are surely more elegant ways to highlight this.

The structure isn't the most original, but Coulombeau, a 27-year-old who won Route's Young Author competition, handles it deftly, and the central event is suitably thorny. Characters' accounts differ on everything from each other's deep-seated psychological motivations to recollection of details, such as the colour of an ice lolly. Truth is slippery, many-sided, and further blurred thanks to the passage of time.

Their parents, the priest and the police are given voice too – and they're just as conflicted. Two deeply divergent accounts of an affair, for instance, prove that it isn't only kids who don't know what's going on. The reader is taken convincingly in one direction then the other – implying that ultimately, the only truth we ever know is what we feel to be true, even if that is a product of self-delusion.

Rites is formed of many short chapters, keeping it crisp and brisk. The loss of virginity isn't recounted till half way through, and while Coulombeau is good at building tension, there's mercifully little titillation. It's a candid but not salacious scene, and these matter-of-fact recollections feel much how a teenager would report it. She's very good on teen logic in general, making fully plausible the shifts in affection, allegiance, even desire, of her young characters, and showing how these shifts can be both terrifyingly quick and deeply felt. It's convincing, and never patronising, which is impressive as she's operating through that double perspective: adults looking back on themselves.