Two civil wars have shaped the USA's self-image. The second, the war between the states, shows America going through hell to achieve a moral goal, and has been the focus of constant fictional reimaginings. The first, though, the Revolution, is the country's founding myth. Its images (the shot heard round the world, Washington crossing the Delaware, Valley Forge) are all iconic, and it has hardly ever been reshaped by fiction, perhaps for fear of damaging that heroic myth.

To an extent, therefore, C.C. Finlay's Traitor to the Crown trilogy, which recasts the Revolutionary War as a war between magics, breaks new ground. But only to a limited extent: the myth remains resolutely intact throughout.

Finlay is enough of an historian to know that the truth was not quite so plain, but whenever his story brings him to a conflict between history and myth, he prints the myth. For instance, two brief, incidental scenes, in the second volume, A Spell for the Revolution, and the third, The Demon Redcoat, show us that he is well aware that freedom in the Revolutionary War was a relative concept. Most blacks chose to fight with the British, because the British promised them freedom (a promise which, even in defeat, they went some considerable way towards fulfilling, setting up a free black colony in Nova Scotia), while the colonists, even the resolutely libertarian New Englanders, emphatically did not. So, in the aftermath of battle, we see one black slave crossing the line to the British side; and later, black refugees are wishing for a British victory. And yet this is offset by the fact that the only people we ever see mistreating slaves are on the side of the British. All our heroes are opposed to slavery, there's an ex-slave working with the good guys, and the American slaveholders we see (such as George Washington) are all noble. If you weren't paying attention, you could almost get the impression this was a war to free the slaves.

This isn't the only occasion where issues are fudged. A brief quotation from a letter in the third volume, The Demon Redcoat, reveals that the new American government has removed the right to vote that women property-owners in Massachusetts and elsewhere had previously enjoyed. This elicits a brief grumble, but does not diminish by one iota the fervor with which all the strong women in these novels support the cause. Strictly speaking, Finlay plays fair, but still manages to distract the eye from anything that may seem to undermine the glory of the Revolution.

In truth, of course, it was never that clear cut. As fighting began, best estimates suggest that around two-thirds of American colonists remained loyal to the crown and opposed the aims of the revolutionaries. They came from all walks of life, but somehow the only ones we encounter in these novels are smug, rich, greedy and distinctly unappealing, or else they are murderous perpetrators of what, in another age, we would call war crimes. And the prominent voices in the British parliament in support of the American cause are silent here (the British supporters we encounter in the third volume are not so much supporting America as opposing a common enemy). But the biggest fudge comes in the very raison d'etre of this trilogy: witchcraft is somehow made out to be profoundly Christian.

I don't object in principle to the way history is used as a plaything in these novels, particularly when the history in question has been so thoroughly mythologised that it is hardly anything but a plaything to start with. But it is distracting. When American victories snatched from the jaws of defeat at Bunker Hill or Trenton are revealed to be the result of magical manipulation, or when George III (a surprisingly sympathetic portrait) is shown to be not the tragic victim of porphyria but a subject of demonic possession, the actual suffering and heroism of real men and women seems somehow devalued. I do not suggest for a moment that such is the intent of C.C. Finlay, any more than I suspect it is the intent of any of those other authors, such as Naomi Novik or Susanna Clarke, who suddenly seem to be making a habit of overlaying fantasy tropes on real historical events; but such is the effect, at least for this reader.

Actually Finlay manages to avoid the worst of these effects in the first two volumes by making the historical drama of the Revolution and the fictional drama of the witchcraft tangential to each other, colliding head-on only in climactic set pieces (Bunker Hill in the first book, The Patriot Witch, Trenton in the second). The third volume is considerably less successful because, in escalating the menace and trying to build towards a resonant cataclysm, the whole enterprise slips into silliness. But I'll come back to the third volume shortly.

We begin with Proctor Brown, a diligent, hard-working, ambitious, no-nonsence Massachusetts farmer, everything, in fact, that the New Englander imagines himself to be (do I really have to point out every example of mythologizing in the trilogy?). Proctor can also do a little scrying, a minor talent inherited from his Salem forebears, but such proof of witchcraft is kept secret for fear of a renewed pogrom. Proctor is also a Minuteman, one of the militia called out when British forces approach Lexington. With his scrying talent he sees a charm on a British officer, and accidentally fires the shot heard around the world. (Do I also have to point out all the coincidences that abound in these books, more even than there is mythologizing?)

Having started the Revolutionary War (and after fighting bravely at Concord), Proctor then effectively retires from the war for a while. Trying to understand his magical talent, he accidentally (the young Proctor is very accident prone) releases a powerful witch, Nance, who has been working on behalf of the British. But this also brings him into contact with a secret network of American witches who have, in a bizarre alliance with the Quakers, been operating an underground railway spiriting witches away from persecution. In a later volume this is specifically made out to be the model for the underground railway that helped escaping slaves to freedom, though that didn't actually come into existence until several decades after the events narrated here. (Nor is this the only pre-echo of the Civil War: several of the more resounding statements made during the course of the trilogy recall more famous utterances from that later war.)

Proctor's encounter with the witch network introduces him to Deborah, a more powerful witch, and when their hideaway, The Farm, is attacked by Nance, killing Deborah's parents, the two have to venture into British-controlled Boston to face their enemy. For the remainder of this first volume, the first stages of the Revolutionary War provide little more than a backdrop to the main but secret struggle, between the two young American witches and the more powerful, pro-British Nance. It seems little more than a coincidence that the outcome of this struggle lifts a curse on the American forces and hence allows them to snatch victory at Bunker Hill.

More significantly, Proctor and Deborah have uncovered the existence of the Covenant, a centuries-old conspiracy of witches who are lending their formidable power to the British cause in America. This sets up the second volume, which follows almost exactly the same structure as the first. The Farm, which has gone from being a haven for witches to a training ground, is again attacked. This sends Proctor and Deborah behind British lines once more, this time in New York, where their struggle against a more powerful magical force will again, almost coincidentally, lift a curse from the American forces just in time for a victory at Trenton. By this time, a year on from the first volume, both Proctor and Deborah have increased their power, though the enemy they face is also considerably more powerful than Nance had been. This time, also, the romance between the pair that had been implicit in the first volume is now explicit. The novel ends with marriage.

The problem with all such works as this is escalation. The need to make the threat bigger with each successive volume, the need to make the consequences greater with each successive volume, turns the relatively low-key magic in the first two volumes, into something on a near-cosmic scale. Each spell has a personal cost, so our heroes are soon enduring increasingly extreme self-inflicted tortures in order to call up each new spell that is always bigger than anything they have conjured up before. Entire weather systems clash like battle-hardened battalions.

In The Demon Redcoat the pattern is, of course, the same as before. The Farm comes under attack, this time a direct threat to Proctor and Deborah's new-born daughter. So Proctor again sets out behind enemy lines, this time to Britain itself, in order to combat the Covenant directly. And since the imperial threat he must face down is so much greater than any so far witnessed, then so Proctor's own magical talents have, in the scant two years between volumes, expanded to a degree undreamed of by our original New England farmer.

One of the other inevitabilities of a work like this is that various famous historical figures will have walk-on parts. In the first two volumes we meet Paul Revere, George Washington, Nathan Hale, Alexander Hamilton and Tom Paine; but such a relatively mild case of celebrity spotting is put to shame by the parade of famous faces who march through The Demon Redcoat. Proctor travels to Europe in the company of John Adams (and his two sons, including another future president, John Quincy Adams); in Paris he stays with Ben Franklin, who of course has a mischievous twinkle in the eye and obliquely hints that he knows all about witchcraft; in London we run into Lord Gordon (of the Gordon Riots, which again prove to be the product of witchcraft), future Prime Minister Lord Shelburne, King George III, and even a young William Blake. But Proctor's main contact in Britain is another real though rather less celebrated figure, Thomas Digges, who just happens to have been not just a genuine American spy but also a direct descendant of the mathematician and cosmologist Thomas Digges—the first person to posit an infinite universe, and a student and colleague of the Elizabethan scientist and mage, Doctor John Dee. And lo and behold, who should turn out to be the leader of the Covenant but that powerful magician Doctor Dee, having discovered the secret of immortality.

It is in the way of things that the complex and rather tragic figure of John Dee should thus become a comic book villain lusting for the blood of innocent children. We shrug and accept these things. But what really doesn't make sense is the climactic battle. Every glimpse we have of Dee sees him effortlessly commanding immense power even on his own, and he can also draw on the power of the rest of the Covenant (which we are told has an inner circle of 12, like the disciples, though we never see more than six). Even the vastly inflated potency that Proctor and Deborah have acquired between volumes should leave them no match for him. Which means that the final conflict is more risible than dramatic: Finlay has so escalated the story that he has left no space to allow this very traditional romance to turn out the way it has to and still make sense.

I must stress that this is not a bad trilogy. It is a quick read (I got through all three books in roughly the time I would normally take on one), quite gripping in its way, and the characters are attractive. It just feels slick and slight, as if the needs of the popular fantasy story have overwhelmed the dramas and challenges of the gripping historical story that forms its backdrop.

Paul Kincaid is the coeditor of The Arthur C. Clarke Award: A Critical Anthology, and the author of the Hugo-nominated collection of reviews and essays, What It Is We Do When We Read Science Fiction.