The Discoverer, By Jan Kjaerstad trans Barbara J Haveland

The Discoverer completes the trilogy to which Norwegian writer Jan Kjaerstad's The Seducer and The Conqueror belong: an enormously ambitious undertaking about an enormously ambitious man – and, beyond him, about ambition itself and humanity's ambiguous need for it. The matter of all three novels – which contain overlaps, revisitings, and some mind-bending contradictions, with each account plausible - is laid out baldly in the first novel's first chapter, "The Big Bang". Jonas Wergeland, who "has risen to heights of fame which very few, if any, Norwegians have ever come close to attaining", returns from the World's Fair in Seville (1992), to his house in Grorud, the Oslo borough in which he grew up. And there, on his living-room floor, he finds his wife, Margrete Boeck, venereologist and mother of his daughter, shot dead.

Wergeland is charged with the murder, found guilty, partly through testimony from his own clergyman brother, Daniel, and receives a custodial sentence. None of the novels proceeds linearly, nor is there one consistent narrator. The Conqueror, after the first book's tributes to his boundless imagination and sexual inventiveness, presents a far more troubled and troubling Jonas. It makes us pretty sure he must have dispatched the woman he so loved. But in The Discoverer we come – via Jonas himself and his devoted daughter, Kristin – to a different conclusion that exonerates this pre-eminent Norwegian, whose main failing may have been precisely that pre-eminence.

But have we reached the truth of the affair? Is this third book the final version? By no means, the author told me recently. Like Durrell's Alexandria Quartet, his trilogy asserts relativity. In one sense only is The Discoverer final: Kjaerstad will write no sequel.

What has earned Jonas Wergeland his mega-fame is his work as a television director of daring and insight, in particular a series of 21 programmes, Thinking Big, dealing with famous Norwegians who both put their country on the world map and affected their own compatriots' view of themselves: figures such as Grieg, Ibsen, Sigrid Undset, Amundsen. Thinking Big eschewed conventional perceptions and, after intense work on Jonas's part, depicted instead seminal moments in their experiences when they felt sufficiently challenged to venture beyond familiar patterns of behaviour and thought.

The programmes are described in compelling detail, and rightly, for their governing ideas and his visual realisation are as essential to Jonas's story as his personal relationships and sexual exploits. That on Grieg is Jonas's favourite, with its shot of the 35-year-old composer in a bath understanding that he must now discard heavy Germanic forms and return to the atavistic simplicities of Norwegian folk music. That on Ibsen (retold in The Discoverer) gives us the writer confronting the great dome of St Peter's in Rome, and feeling emboldened to attempt the titanic in Brand and Peer Gynt.

So egalitarian are Norwegians, thinks Kjaerstad, that they have difficulty in accepting the outstanding, the genius, even while honouring their great men and women as secular saints. In The Conqueror, Wergeland appreciates this: "The message Jonas Wergeland wished to convey was a hopeful one: one, just one, great thought can be enough."

You can see Jonas as seducer, as conqueror, as adulterer, as cuckold, as killer, as victim, as (literally) a prisoner. But what is truly important is his loving reception of flashes of inspiration that irradiate his subjects and will infiltrate his galvanising programmes. Norway itself has, thanks to North Sea oil, its own exceptionalism now, yielding satisfactions and problems. The various reverses of Jonas's fortunes mirror this.

In The Discoverer Jonas, his prison sentence served, journeys down the Sognefjord, for him a microcosm of his country: august, awesomely beautiful, unfailingly refreshing. From either side, other fjords, lesser in size but with individual fascinations, run out. So can we envisage Jonas's own life. Tributaries demand attention, but essentially it consists of one long, solemn progress to the inescapable and measureless: the open sea. Failings and upheavals suddenly turn unimportant; what matters is the spirit in which the main voyage is conducted.

The voyage that The Discoverer will impel, thanks to Barbara J Haveland's lively, fluid and at times sparkling translation, is a return one, to the beginning of the whole trilogy – a work so ample in its riches that further discoveries are inevitable.