Like any novelist on the brink of publication, Russell Banks has been feeling a little apprehensive about the reception for his latest book, Lost Memory of Skin. But Banks's anxieties – acknowledged in a recent interview – had a slightly sharper focus on this occasion. He wasn't just worried about how his prose style would go down, but about how his subject matter would.

That's because one of the leading characters in Lost Memory of Skin – let's avoid the word "hero" for now – is a convicted sex-offender, and one of Banks's purposes in the book is to question the societal hysteria that such people arouse.

Since the terms of his probation won't allow the Kid, as the character is known, to live within 2,500ft of any place where children regularly gather, he finds himself, along with an assortment of other social pariahs, living underneath a causeway on the Florida coast. The novel had its origin, in part, in a newspaper story about just such a community – located beneath a highway that Banks could see from his Miami house.

By coincidence, the publication of Banks's novel roughly coincides with the release of Michael, Markus Schleinzer's film about a Josef Fritzl-style child-abductor who has imprisoned a 10-year-old boy in his cellar. In both cases we're obliged to spend time with characters that we perhaps wouldn't usually choose to, characters, moreover, who fit a peculiarly modern template for a monster. But the two treatments of the subject are very different. Whereas Schleinzer's paedophile (there are strong hints that he's not just keeping Wolfgang in the basement for company) is seen from the outside, we have access to the Kid's interior thoughts.

And that raises an odd and uncomfortable possibility. A film might conceivably have a paedophile or a sex offender justifying his or her tastes – but it would find it much more difficult to make us share them. A novel, on the other hand, offers a different kind of intimacy, with other ways of thinking. As it happens, there's a passage in Banks's book where just such a thing seems to be happening. The Kid is sitting on a street bench when he's teased and taunted by two young girls on roller-skates, both of them around 14 or 15 and both of them dressed for a Miami summer, which is to say barely dressed at all. The Kid is both terrified by their presence (because of his bail conditions) and excited by it – and Banks's prose dances between panic and thrill in a way that inevitably co-opts the reader. In the end this sequence modulates into a saving fantasy, rather than an incriminating one – as the girls appear to transform into brightly coloured parrots and flap away. But it has made one of its points before this happens – about the odd contradiction of a society which happily sexualises young girls and is then appalled when they're regarded as sexual beings.

Banks's book isn't any kind of apologia for paedophilia. But it does want to argue that our reactions to sex-offenders might need to be more nuanced. Indeed, sex-offenders are described at one point as "canaries in the mine" – the suggestion being that the compulsions of paedophiles (and a rise in the rates of sexual offences against children) is a warning signal of other kinds of social pathology. It's brave, given the climate of hysteria that surrounds such crimes.

But there's a limit even to Banks's courage. The Kid, it eventually becomes clear, never did anything and certainly was never a child molester. He has also been effectively desexualised by shame and shock, and is himself a victim (of parental neglect and loneliness). It comes to seem almost bad luck that he has ended up on the wrong side of that deep divide between the intolerable and the ultimately redeemable. (It's a less courageous account of the offence, in fact, than Alan Bennett's 1998 Talking Heads monologue Playing Sandwiches, in which a convicted child-molester slowly reveals the uncomfortable truth that humans – even quite likeable humans – can do these things, not just monsters).

Still, Lost Memory of Skin does at least acknowledge that the subject needs more imagination than it generally gets. If we're going to tell ourselves stories about sex-offenders and paedophiles there's really not much point in them being simple horror stories. Artists need to take a risk, though one can hardly blame them for being nervous when they actually do.

Boetti's law states that less is usually more

After visiting Tate Modern's exhibition of the work of Alighiero Boetti last week, I found myself moved to propose a predictive generalisation about conceptual art. The exhibition is excellent, but it was the sharp gap between my experience of two of the exhibits that got me thinking that there must be some ratio between the success of conceptual art and the concept that gave it birth. Boetti's Law was the result, which states that there is an inverse relationship between the complexity of the explanatory rubric for a piece and the satisfaction the resulting work delivers. So, take Boetti's Viaggi Postale as an example. As far as I can understand this consisted of sending badly addressed letters to celebrated artists and collating the returned envelopes, though there was something elaborate about enveloping the envelopes in still larger envelopes that I couldn't be bothered to read, because the pieces themselves were so dull. The art on the wall was proof that a process had been conducted, and little more. By contrast, a giant drawing called I Sei Sensi required no explanation at all for its impact. Its textured surface was composed of countless small strokes of blue ink, and to work out how the un-inked apostrophes on its surface spelt out a message. But it had blossomed beyond an account of its making to produce something much richer. It wasn't just evidence it was art. Boetti's Law in action.

The movies that live by night

What's the darkest film ever made, talking in terms of light-exposure meters? Some ground rules here. Science fiction and horror films aren't really eligible, I think, since so many narratives depend on the effects of nightfall. And I'm going to rule out Rodrigo Cortés's excellent thriller Buried, which takes place inside a coffin. What I'm looking for is real-world, real-time movies with the greatest likelihood of inducing Seasonal Affective Depression in a viewer. I saw a front-runner last week in Pablo Trapero's film Carancho, a bleak account of a Buenos Aires ambulance-chaser in which you don't see daylight until about an hour in, and even then it's only glimpsed out of the corner of the camera's eye, often through grimy windows. And though there is a burst of evening sunlight right at the end of the film, given what it shines down on it can hardly be counted as a mood enhancer. Carancho edged out my previous number ones in this specialised field – Oliver Hirschbiegel's 2004 film Downfall, a work of exemplary murkiness only let down by the occasional excursion into the garden of Hitler's bunker and the shattered streets of Berlin, and Martin Scorsese's Bringing Out the Dead, about a night-shift ambulance worker. But I feel sure there must be other masterpieces of the tenebrous out there.

t.sutcliffe@independent.co.uk