This book does not hide itself behind a coy title. Jack Wolf's extraordinary 18th-century story does exactly what it says on the cover. It's a tale, in the grandest sense of the word. It's raw, at times even extreme. It explores elegantly the eternal dialogue between the head and bones. And it's quite startlingly, and beautifully, bloody.

The narrator is Tristan Hart, the son of a Berkshire squire growing up in what should be gently bucolic circumstances. But Tristan's own mind keeps getting in the way, with its tendency to run away with itself and to see goblins and Gypsies and elves prancing on the lawns outside. For Tristan, the countryside has rather too much of Faerie in it, and the Uffington White Horse looms symbolically large. What is real, and what is fancy?

This is the question which defines the story, because Master Hart is Mad, but he is also a Genius, obsessed by the inner workings of Nature's creatures, determined to understand the interfaces between Body, Mind and Soul  "Whatever the Condition of the Soule within, the Human Body was a Machine, susceptible of Damage, Illness and Decay  but also of Repair." And if that were not enough, he is also a sadist of poetic intensity, for whom Pain is both Viagra and Vision, something he will "measure and circumscribe"  "at every Squeak and Whimper, the internal Anatomy opened up before mine inner Vision, clear and sharp as an Engraving".

One should apologise for the infestation of initial capitalisations, but it is infectious. The entire book is written in the authentic Voice  sorry, voice  of the 18th century. At first this smacks of affectation: after 20 pages, one asks what is the point of an imitation of Tristram Shandy when one might just as well read Tristram Shandy. After 50 pages, one is swept along by the book's unrelieved energy.

Tristan Hart is allowed to develop his interest in anatomy, moving to London as a young man to study under the great Scottish anatomist and physician William Hunter. The London chapters bring us big and brutal setpiece scenes under the knife and the whip. Cadavers are dissected, cancer is dug out of living flesh, and Tristan's sadistic tendencies are sketched out upon the flesh of Covent Garden prostitutes.

All of which might be a little strong for some tastes, and there is no escaping the fact that this is a vicious, extreme book. But it was a vicious, extreme time; there is great beauty in many of these scenes, and great humanity as well. Wolf skilfully weaves the philosophical questions of John Locke  specifically, what the Mind is and how it conceives of itself  with the coarser and bloodier matters of skin, bone, blood and vein. Is the body a mere mechanism? Is madness a result of broken workings, or something more metaphysical? And what  and where  is the Soul?

Placing a first-person narrative at the centre of the 18th century gives these questions new life. This was a time, after all, when old superstitions and new science were held in equilibrium. The 150 years between Thomas Fairchild's creation of the first hybrid plant and the publication of On the Origin of Species saw the world classified, explained and experimented upon in a wild rush of discovery. But it was also a time when an act forbidding accusations of witchcraft was thought necessary, and natural philosophers still justified their investigations into the deep past against the ludicrous timeframe established by Bishop Ussher.

Putting that struggle between science and superstition into the deranged head of Tristan Hart is a very good idea, and Jack Wolf delivers his tale with passion, precision and poetry. Those of strong stomach and vivid imagination will find glittering delights in here.

 Lloyd Shepherd's The English Monster is published by Simon & Schuster.