'A Novel of the American Revolution.' The eighteenth century. Ambrose Tree rides the Lambeth Marshes to Drogo Hall, summoned by an ageing uncle to hear the story of Harry and Martha Peake. Of how the Cornish smuggler and radical poet lost most of his kin in the horrific fire that left him hunchbacked, unable to present his verse in London alehouses save by exhibiting himself as a shambling freak show. And of his surviving daughter, the proud, angry Martha, with her red mane and her father's fiery commitment.

But life above a Cripplegate pub is too much for this poor, battered man and a pathology every bit as monstrous as his deformities hatches. "For as my uncle correctly said, if the world calls a man a monster, and there is nobody to contradict it, then that man, in his own eyes, becomes a monster." When his attentions turn lasciviously toward his daughter, Martha is forced to flee to the sanctuary of Lord Drogo, a nobleman and anatomist with a powerful professional interest in her father. After one final, unspeakable act, however, the time comes for Martha to strikeout for the revolutionary fervour of the New World.

For an author who embraces the unreliable narrator - the voice of his brilliant second novel Spider is so specious it rewrites the rule book every time you turn the page - Martha Peake looks to be little more than a distillation of form. With both Tree and his uncle to hand the book effectively engages two authors, neither fully trustworthy: "It is a black art, the writing of history, is it not? - to resurrect the dead, and animate their bones" And soon it's clear, by his own admission, that Tree no longer simply reports but uses scraps of evidence on Martha's progress to forge his own tale, "in a very frenzy of historical reconstruction."

All of which should be grist to McGrath's mill. So what is it that gifts Martha Peake the vague air of disappointment?

In the past McGrath has tended to see the 40s and 50s as his parade-ground. Spider, Asylum, the war-time stylings of his masterly Dr. Haggard's Disease - there is a fetid, heightened, but ultimately recognisable quality to McGrath's world; there is the distance of history, but not so far that we lose focus. In this book, though, it's Dickens, Le Fanu and, especially, Wilkie Collins that serve as touchstones. Many seem enamoured of this great mouldering wedding cake, but one cannot help but find disappointment in McGrath's willingness to embrace the Gothic (as opposed to the merely gothic). It's easier to hide in the shadows of the mist-shrouded country house than the tiled hospitals and terraced housing of the recent past.

It's not all loss, though. For even as he surrenders to the easy seduction of the historical novel, the precision of McGrath's prose shines. It is honed with a rare but readily accessible placing of word and image. His evocation of America on the brink of its birth is remarkable. But equally it's noticeable that, for all the grand panoramas, McGrath is only able bring closure to his tale back in the crepuscular chambers and passages of Drogo Hall. Every monster, he says, goes home to die.