Joanne Harris shot to fame with the film of her sensuous, romantic novel Chocolat, and some of her fans may well be taken aback by her latest offering.

Blueeyedboy is told in the form of a weblog, apparently written by a serial killer.

She said: “My hero — B.B., or Blueeyedboy — is a man in his early 40s who still lives with his mother, about whom he has murderous fantasies, which he translates into fiction, and posts to a website called badguysrock."

She says it was written after she endured "a bad time" in her life.

“I found I didn’t want to write, and spent far too much time online, hanging around various sites and searching out ever more ingenious ways of evading reality.

“Under a pseudonym, I made a number of online friends, wrote a great deal of fanfic, and began to take an increasing interest in the way people interact online, the communities they create and join, and the way they choose to portray themselves.

“I began to understand that the small communities that have always informed my writing also exist in the virtual world, with the same little cliques of insiders, outsiders, gossips, liars, exhibitionists and bullies as in the ‘real’ world.

“I understood too, how emotionally dependent people can sometimes become on their virtual friends and their virtual communities."

It is a puzzling book, and the most remarkable thing is that it is written by a woman. Not many female authors would include six playlists of music enjoyed by the narrators, including bands like Black Sabbath and Nirvana.

She said: "The musical tracks are all carefully-chosen to reflect the mood of each entry as well as containing clues — some more obvious than others — which, put together, make up a series of six playlists (one for each section of the book) which serve as a mini-summary of the plot.”

Without giving anything away, the final track is Abba's Winner Takes it All.

Although B.B. is “devious, cynical and quite self-consciously cruel,” she rather likes him.

She said: “He is the product of an appalling background, a controlling mother and an imperfect education.

Still living at home at 42, a janitor in a local hospital, he hates himself, hates his life and yet he has managed both to retain his sense of humour and to re-create himself online as the person he would rather be, instead of the born loser he really is.

“He inhabits a kind of fantasy world, which occasionally erupts into real life, with unpredictable consequences. And yet he is deeply vulnerable — although whether this is the 'real' B.B., or whether he is simply using his vulnerability as another means to an end, is ultimately hard to say.

“He is, I think, the most complex character I have ever created, and perhaps the hardest to understand.”

She features three times at the festival. On Thursday, March 28, she will give a talk, sponsored by The Oxford Times, while on March 26 she will talk about a visit to Togo organised by children's charity Plan UK, with Kathy Lette, who visited the slums of Brazil, and Deborah Moggach, who went to Ghana.

A former teacher, she has also agreed to chair a debate, on March 24, between Adrian Elliott, author of State Schools Since the 1950s: The Good News, and newspaper columnists Peter Hitchins and Chris Woodhead.