Anointed with holy oil at his coronation at the age of 17, Henry VIII's flesh becomes divine. "I am God's Chosen," he says. "That is the basic fact  irreducible  from which all thinking must begin." HM Castor's crossover novel, VIII, probes the psyche of a man increasingly convinced of his own specialness, yet unable to reconcile this with how circumstances combine against him, and explores the gap between the world and how he chooses to see it. Epic in scale, while told in the restricting view of the first person, Castor's book sets out, in effect, to deliver to the modern reader Henry VIII as unreliable narrator of his own life.

The more I read, the more struck I was by the ambition of this novel. This is well-trodden historical territory where you have to fight your way through clichés of a lascivious, fat-chopped, roaring monarch to reach your own view of him. The decisions regarding what to show and what to skirt over during his action-packed reign are never-ending, and the writer's choices are always going to displease someone: the young and the not-so-young adult, the hard-nosed historian, the fan of the recent TV series, the school librarian. And, of course, you have to have something new to say. On the other hand, what a subject: power, sex, war, religion, destiny 

The driving question VIII asks is: What turned a talented, charming, athletic youth into a morally and physically corrupt monster? By focusing on his early life, Castor is able to suggest how Henry's struggle with his personal demons is played out later, in the larger arena of the state.

Henry was born in the aftermath of civil war. His father did not inherit his crown, but won it on Bosworth Field. The exciting opening to the novel shows mother and son moving into the Tower of London for safety while Henry VII fights off another claimant to the throne.

The fear and uncertainty that hung over the Tudor dynasty during Henry's childhood will undoubtedly have taken its toll: he did not feel safe. His beloved mother, Elizabeth, died when Henry was 12, shortly after Arthur, his elder brother and heir to the throne, died at 15. Crucially, until then, as second son  "spare not heir"  Henry needed to learn to keep a low profile. Indeed, in one of the strongest scenes we see young Henry beaten up by Arthur and his lackeys, with the blessing of his father, after outshining his brother at a public tournament.

In order to depict the growth of the darker side of Henry's psyche, Castor uses (and occasionally overuses) the device of a ghost or vision that haunts him, a symbol of his increasingly fractured soul and his failure to achieve the glorious destiny he hoped for.

This is a book of two halves. The first deals with his childhood and is coherent and satisfying; the second depicts Henry as Tudor monarch. This second half flies by like a night train through a station: we are left with brief, vivid glimpses and character sketches, a gradual build-up of moral disintegration and psychological pain. The stories of his six wives, of the reformation, of his disenchantment with those who served him, are all there, and it is skilfully done, though there were moments, perhaps inevitably, when I wanted more.

Accessible, enjoyable and full of fascinating detail, VIII is a page-turner that encourages readers to eschew preconceptions and to look at this Tudor icon in a fresh light.

 Linda Buckley-Archer's Time Quake Trilogy is published by Simon & Schuster.