Sarah Thornhill, By Kate Grenville

The last instalment of Kate Grenville's trilogy of colonial Australia is both a standalone story and an end to the unfinished saga of the Thornhill family. It offers two discrete reading experiences: those who have read the first in the series, The Secret River, will understand, early on, that this story is one of colonial crime, guilt, and possible atonement. Those who have not will only stop seeing it as a thwarted love story towards the end.

The novel begins as a Bildungsroman, spoken in Sarah Thornhill's voice. She is the spirited youngest daughter of William Thornhill, who has gone from being a thieving convict in London to a wealthy "emancipist" in New South Wales. She falls in love with Jack Langland, (a family friend whose mother was an Aborigine) who she plans to marry, to the horror of her parents. The fringes of the Thornhill estate are populated by hollow-eyed, hungry Aborigines, though the significance of these ghostly "blacks", to Grenville's new readers, is left unexplained for the most part. They are more of a haunting than a real presence.

The explanation – and the central secret - drops like a bomb in Sarah's life 50 pages short of the end. It blasts away any remaining illusions of her family's wholesomeness and re-calibrates the tragic focus in her lost romance.

William's amassing of land and fortune has rested on this past abomination, which now links to Jack and Sarah's fates. For those who have read The Secret River, a thoroughly absorbing bestseller, this last instalment will read like a Greek tragedy in which the sins of the father are visited upon his children and grandchildren. Culpability runs through the Thornhill bloodline, but so too does the possibility of expiation.

The Thornhill children sense, to lesser or greater degrees, that their charmed lives are built on blood money, but to face the fact would mean a surrender of their luxuries. As reality dawns, Sarah reflects: "I'd eaten the good food off the cedar table with the double damask cloth. Slept in the soft beds. Sat in the parlour, never known a day's hunger or cold, never asked where any of it came from." It's a sober admission of unconscious knowledge, and with it, unconscious guilt.

Thornhill's crime, Sarah's guilt and her siblings' blindness, so Grenville's novel implies, is the nation's. There is one Thornhill sibling who rejects his family's wealth and lives among the wronged. This, like Sarah's final act, seems like the noble, and the most difficult, way to atone. If fault is to be found, then it is Sarah's unconflicted acceptance of her inherited guilt, though this is also what makes her heroic.

The book is also about the confused identities of colonisers. Sarah describes herself as "nothing but a blank where the past was" when comparing her sense of self to her husband's proud Irish identity. Grenville has spoken of the limits of writing in Sarah's illiterate voice – her father has furnished his children with wealth but denied them education – yet it comes with its own poetry. After controversy surrounding the historical aspects of The Secret River, Grenville makes clear, in her acknowledgements, that this is both a re-telling of her family's story and a novel. It is both brilliant fiction and illuminating personal history.