Danny Wallace isn’t your typical debut novelist. That is, unless your typical debut novelist has, among other things, already written seven successful non-fiction books, one of which has been turned into a film starring Jim Carrey, and who also presents the morning show on XFM in London to pass the time. Until now, Wallace has perhaps been best known for writing a series of informal, off-hand, not-really guides for the modern bloke such as Yes Man (saying ‘yes’ to everything for a year) and Join Me (accidentally becoming the leader of a cult that believes in random acts of kindness).

Some of these one-off projects appear to be undertaken for, frankly, a bit of a laugh, but there are underlying themes that hint at Wallace’s philosophy, many of which resurface in a slightly different form in his first novel. The main theme in both his non-fiction and, now, fiction is all about ‘seizing the moment’, whatever that moment is. It doesn’t have to be big or grand or lead to riches, fame or fortune. In fact, it’s more likely to result in humiliation, confusion or, if you’re really lucky, love. Which is the central conceit of Charlotte Street, cheekily tag-lined, ‘a heart-warming everyday tale of boy stalks girl … ’ The stalking is pretty mild. And largely ineffective. But then, that’s not really the point.

The idea is simple: Jason Priestley (no, not the one from Beverly Hills 90210, though that is a relevant detail) is standing on London’s Charlotte Street one day when he finds himself holding a disposable camera belonging to a woman he glimpses for a moment before she gets into a taxi and is gone from his life forever. Or at least she would be if he didn’t sort-of, kind-of, not-really try to track her down. Jason has been recently ditched by Sarah, now happily engaged to Gary, who represents everything Jason hates. He’s living with his dreamer best mate Dev, who runs a retro gaming shop no one ever visits. He’s writing sarcastic reviews for London Now, a rip-off of the free papers you get on the Underground and probably don’t read.

It’s all a bit depressing really – unless you have a bit of the romantic in you. Against the odds, and seemingly without any coherent plan, Jason and Dev set about finding this woman from Charlotte Street, starting out by developing her photographs and examining them for evidence. ‘There are things you can do to have more fun in life,’ says the author, sitting in Glasgow’s Royal Concert Hall. ‘You just have to do them. Even if often you end up making mistakes while you’re trying.’ Well, Jason and Dev certainly do make a lot of mistakes along the way. In fact, they hardly make a right step for several hundred pages.

When I met up with the Dundee-born Danny Wallace, he’s at the back end of a hectic week of promotion (and running late for his taxi to the airport), but he’s full of the kind of energy that zips through his books. He’s keen to talk about the novel’s details, and clearly buzzing from the reception it’s already had (the book has sold in 15 countries so far and was only published in mid-May).

Essentially, Charlotte Street is a commercial romance about hope and ambition, set among characters who mean well but aren’t really that good to each other. In fact, the cast are constantly letting each other down, failing, not being able to stay sober for very long, and then having to apologise. So what is it that holds them all together? ‘Well, we all let each other down, all the time,’ says Wallace. ‘The main thing is, Jason does things he thinks are right, and he always has hope.’ He stops to think. ‘This book is packed with hope. I hope. And I say this hopefully! It’s the same as the message in my other work really: life can happen to you, or you can make life happen. Jason does do that. In the end. Which is why I say it’s packed with hope.’

It’s at this stage I realise that talking to Danny Wallace is almost the same as reading one of his books. As well as being similar to his conversation, the novel’s tone is recognisable from the non-fiction that preceded it. So, I wondered, was it easy to transfer from one form to the other? ‘There was a lot I took from the previous books, yes,’ he says. ‘I like to get on with the reader, and Jason wants to be liked by the reader too, so there was that in common. Also, I prefer to write like I speak, but posher. You know, the way you might talk to your girlfriend’s mum.’ And how’s that, exactly? ‘With a few bigger words, and a few less swears.’ That’s a fairly accurate description of Wallace’s style, though it’s not always that well-behaved.

The story is often cut up with excerpts from Facebook messages, little games Jason plays inside his head, and also his descriptions of other characters in the book based on the report card he might give them if he was still a teacher (Jason used to be a teacher. And then stopped. And then became one again). The most unflattering of these report cards is saved for Gary, Sarah’s fiancé, but most characters get laid into at some stage. As Wallace says of his protagonist, ‘at the start of the novel, Jason’s one of those guys who mistakes cynicism for wit.’ Which is something his creator could never be accused of. There’s not an ounce of cynicism in him.

There are many other things that mark Danny Wallace out from the literary crowd. For example, he has brought to life the fictional band in the novel, The Kicks, inviting real bands to write a version of their (imaginary) hit ‘Uh Oh’, with a whole series of them coming to XFM to perform on his show. What else? Well, the much-derided London Now has been made real too, with Wallace handing out 50,000 copies on the streets of the capital, all the pages full of clues and in-jokes from the novel.

And to finish off the week’s tour, he was due to conduct a signing in a pub on Charlotte Street itself. On a Friday night. At going-home-from-the-office time. It’s the kind of can-do approach to publishing that some writers get tired just thinking about, but Wallace is most comfortable including others in his work, opening it out like it was one of his non-fiction adventures. And it’s the most appealing feature of his writing. It also makes sense of how he’s been able to build an international Karma Army over the last decade.

Let’s return to Jason and his report cards: if Danny Wallace was a teacher, and Charlotte Street was one of his students, how would he describe his own novel? ‘How’s this?’ says Wallace, carefully considering his options (and perhaps also his publicist). ‘Does its best. Has its flaws. But ultimately has the makings of a very good pupil. See me.’ Then he breaks out into a large grin. That kind-of, sort-of, not-really humility will serve him well in Edinburgh.

Danny Wallace, 18 Aug, 8.30pm, £10 (£8); Rodge Glass (with Teddy Jamieson), 20 Aug, 8pm, £10 (£8). Both events at Charlotte Square Gardens, 0845 373 5888.