A sultry August in Sicily in 1999 provides the initial setting for Marina Kemp’s powerfully compelling second novel. The court of the revered novelist and patriarch Don Travers – his four children; his silent, apparently surrendered wife Lydia; and a revolving guestlist of the great and good, the influential, the useful and the up-and-coming – is in situ at Il Frantoio, the rambling villa the family takes every summer.

At 10 years old, the youngest Travers daughter, Nemony – feeling left out, as youngest children often do – is our first and principal narrator. The second is a young writer, Zoe Goodison, whose first novel has recently been published to high praise. She has been brought into Il Frantoio’s charmed circle by Don, whose interest in her may or may not be sexual. Zoe is alienated from her background, in a toxic relationship, ill-at-ease, prickly, proud and insomniac. Like Nemony, she inhabits the storyteller’s position on the edge of things.

The summer begins as usual, with the siblings – 19-year-old Tree, followed by Malachy, Etta and Nemony – circling their rivals, the guests, to assess each as friend or foe, pretentious or annoying, inconsequential or dangerous. It is a pattern that has always knitted the children tight, but this year is different. Their mother, Lydia – who escaped from an Amish-style community at 19, but in subjugating her needs and desires to those of her family seems never quite to have left it behind – has cancer, and this could be her last summer. Moreover, the beautiful, irresistible Tree is no longer a child, and as she begins her negotiations with the adult world the siblings’ loyalties are placed under pressure, with consequences that turn out to be shattering.

We rejoin the narrative in London 20 years on: at Il Frantoio, Don had said with eyewatering condescension to Zoe that “that’s when you’ll get really interesting”. The Travers family has scattered in the wake of a catastrophe whose rumblings were felt that long-ago summer, but whose origins and mechanism remain obscure. Nemony is dealing with the stress of new motherhood, made more intense by a faltering relationship and the memory of her own self-sacrificing mother. She encounters Zoe, now a successful novelist living in enviable freedom close to the Travers’s childhood home, and is apparently befriended by her. But Zoe has a narrative of her own to pursue, and as the two grow close what remains of the precarious unity of Nemony’s family is threatened with violent and irrevocable rupture.

Novels about the writing of novels carry some risk. They can be self-regarding, they can be bewildering, and they can be slyly exacting, forcing the reader to retrace their steps in pursuit of objectivity while gleefully manipulating the only truth: that is, that this is all made up. Kemp – who was shortlisted for the Sunday Times Young Writers’ award in 2020 for her debut, Nightingale – deftly avoids the first two of these pitfalls while triumphantly embracing the last.

To whom does the truth of lived experience belong, Kemp asks. If Lydia chooses not to speak of the damage inflicted on her, does anyone else have the right to expose it? If the same family secret inspires rage in one victim and shame in another, whose is the copyright? And if Zoe tells the best story, can she co-opt the Travers family’s unhappiness to her own ends?

The tension Kemp applies to this tightrope is the key to her success in walking it. Holding all her narratives in balance and leaving final judgment to the reader, she is meticulous and unsparing in her dissection of the creative process and its casualties: she exposes Don as an ageing Prospero and a gaslighting tyrant, but she also lays bare the ruthlessness and treachery that Zoe employs to get the access she wants. And our reward is the miraculous potency of the written word, the tale shaped and told through Lydia – who barely speaks even to those she held closest, but does finally set her story down in writing – and through Kemp’s own masterly skill.

• The Unwilding by Marina Kemp is published by 4th Estate (£16.99). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply