Nick Hornby is one of that select group of writers whose new books are keenly anticipated by followers in the way fans of a singer/songwriter await a new album. So it's appropriate that, in his first novel for four years, Juliet, Naked is the title of just such an artifact: a long-awaited release from the reclusive cult musician Tucker Crowe.

Duncan is a Crowe obsessive or "Croweologist" whose empty life is given meaning through his geekish investigations into the Crowe myth. Hornby, as a self-confessed musical anorak, is on familiar ground here. Duncan's self-satisfaction revisits some of the territory covered in High Fidelity, as we encounter another tragicomic musical obsessive whose intimate knowledge of his chosen specialist subject leads him to assume a smug superiority over anyone who doesn't share his passion. I had a friend who refused to be told that the perfectly harmless indie band Hefner were going to be but a footnote in the annals of rock. I myself remain entirely convinced of the true greatness of Wilko Johnson-era Dr Feelgood. Hornby understands perfectly the world we inhabit.

Duncan's long-suffering partner Annie has come to her own appreciation of the Crowe oeuvre in an attempt to have at least one bond with her hapless boyfriend - even if it means holidaying in America in order to visit the toilets of a Minneapolis club where the elusive musician had some sort of epiphany. Again, Hornby sure-footedly documents the hold that a Fever Pitch-like obsession can take. Annie, who hopes for the child that Duncan seems unwilling or unable to give her, must once have found the Crowe fixation cute. Now it would seem tiresome were it not for her own regard for this little-known but highly rated rocker, who hasn't been heard of since 1986.

That was when he released his best work with the album Juliet. The small but committed band of uber-fans, united inevitably in a chatroom, have all but given up on hearing of him again when a new album, Juliet, Naked, suddenly materialises. Basically demo recordings and song sketches for his 1986 masterpiece, it is the subject of an online eulogy by the besotted Duncan. Irritated by both the record and Duncan's blinkered response to it, Annie posts a more realistic review of its glaring inadequacies. The aim of this article is to give Duncan a reality bite, but an unexpected email response comes from someone who shares her honest assessment: Tucker Crowe.

A relationship evolves from this point, and though it seems in some ways unlikely that a mere fan would be able to connect with an artist in this way, stranger things have happened. Ask Gary Numan and the former "Numanoid" who is now his wife.

Perhaps the only problem with this immensely readable book lies with its very subject. To understand why a recording artist would inspire devotion of this kind, we would really need to have heard their music. If we are asked to empathise with someone rhapsodising about a landscape, or a city, or the ocean, or someone's beauty, we have reference points in our own lives that enable us to do so. It's harder to hear songs that have never been written, tougher to believe in a rock star who never existed. When we encounter references to real songs and bands in the context of fiction, our knowledge of that music tells us something about the characters in the prose. Here, you have to take a leap of faith and believe that Tucker Crowe is as good as Duncan thinks he is. Early on this is slightly troublesome, as the inadequate Duncan doesn't appear to be someone whose judgment you would gladly trust, but once you make the decision to accept what he's telling you, you're taken on an easy and enjoyable ride.

This is a lean book - 250 pages including emails and chatroom extracts. In an age when all we seem to need to know about famous people can be gleaned from their Wikipedia entries, this seems entirely appropriate. There are, however, few characters who live and breathe beyond the central quartet of Duncan, Annie, Crowe and his son Jackson. When they all meet up for a seaside stroll in Gooleness, where the bulk of the action takes place, it's almost as if they're the only people living there. But so exquisitely are the main characters drawn that their interplay is quite engaging enough.

 Mark Radcliffe's Thank You for the Days: A Boys' Own Adventures in Radio and Beyond is published by Simon & Schuster

In many ways, the premise for this, Nick Hornby's sixth novel, seems typically enticing. In a washed-up British seaside town with the fittingly dead name of Gooleness, Annie and Duncan have stewed for 15 years in a relationship that feels similarly lifeless, partly because it contains a third person.

Duncan has long been obsessed with a 1980s American singer-songwriter called Tucker Crowe who, after Juliet (his 1986 "legendary break-up album"), sank mysteriously from view, never recording or appearing in public again. This has only intensified the admiration of his mainly male, fortysomething fanbase.

But even though the website that Duncan runs for fellow "Crowologists" has a "latest news" section, for 20-odd years there hasn't been any. So when an advance copy of Juliet, Naked  an about-to-be-released CD of "solo acoustic demos of all the songs on the album, plus two new unreleased songs from the same session"  comes Duncan's way, he is transported to Crowe heaven.

Furious with Annie for listening to the album first, he rushes to post the first ecstatic review on his website. Meanwhile, Annie, whose admiration for Crowe is far more objective, sees Juliet, Naked for what it is: "Juliet but without all the good bits". Irritated by Duncan's unquestioning worship  and increasingly aware that she may have wasted 15 years with this one-track man  she posts her own, less adulatory review. When she immediately gets an appreciative email back from Tucker Crowe himself, she's not the only one who's shocked  so are we.

I admit I was at first rather hoping that the whole point of Hornby's novel would be that Tucker Crowe would never actually appear. Its likably bleak humour lies mostly in Hornby's pitch-perfect examination of male fandom and the almost sinister way in which the advent of the internet has fed and enabled it. He's every bit as good as you'd expect on the crazed dynamic of the messageboard and the way in which the web has enabled fans to stalk and even, somehow, take possession of their idols from the safety of darkened bedrooms. It's no joke when Annie quips that Duncan knows more about Crowe than Crowe himself. And Hornby knows how such an obsession can haunt a relationship: when Annie observes that she has long accepted the Crowe thing as "part of the package, like a disability", you know all you need to know about life with Duncan.

However, so convincing is the Tucker Crowe who inhabits Duncan's mind that when we meet the real person pushing a trolley around a supermarket somewhere in America with his six-year-old son, it feels deflating. That is Hornby's point  idols are only as big as the fantasies we project on to them. Still, as Crowe establishes himself as the third narrator of this tale, the writing loses its engaging fluidity.

There's nothing very surprising about the fact that Crowe doesn't believe in his own status or that, like Annie, he thinks he's wasted half his life. And it ought to be interesting that, trailing as he does a string of ex-wives and neglected offspring in his wake, he also carries with him the deep, dark secret of what actually triggered that 1986 withdrawal from the world. But somehow, after that build-up, it's not quite interesting enough.

That's not to say there isn't plenty to admire in this novel. No one writes about music, and the emotional space it takes up, like Hornby. And every time you worry he's about to do something really obvious, he swerves away in the nick of time. What could have been a cringingly, soppily romantic encounter between Annie and Crowe is made far more achingly real when, to her frustration, she finds herself behaving like yet another disapproving wife. And the pure deliciousness of the moment when Duncan realises his ex-girlfriend is hanging out with his idol is certainly well-earned.

Hornby has made no secret in the past of his admiration for the simplicity and soul of Anne Tyler's work, and there's nothing in the plot of this novel that I couldn't imagine that writer tackling. But I found myself longing for a little of Tyler's sly ambiguity, for her ability to leave you worrying, hoping, caring. When Hornby tells us what's going on in a character's head, it's not that we don't believe him, more that it leaves us too little to do. I wanted gaps, I wanted subtext, I wanted uncertainty.

Elasticity  a sense that a novel has been written, in part at least, because its author needed to find something out for themselves  is an underrated part of what creates narrative atmosphere and tension. It's also a large part of why we read on. Nick Hornby is an enormously accomplished writer, but next time I'd love to read less about what he's already decided and more about what he still needs to find out.

 Julie Myerson's The Lost Child (Bloomsbury) is out in paperback