I'll admit, giving an unbiased review of Margaret Atwood isn't an easy task for me. This is the author I credit with changing my entire concept of literature, back in my impressionable early teens. The author is part of the Canadian national psyche, and as an ex-pat I've often returned to the familiar landscape of her work, as well as that early realisation of the possibilities of fiction.

There's a slightly hysterical atmosphere in Charlotte Square. In 24 hours, the book festival will be over. Atwood launched her multi-city musical tour to accompany her new novel The Year of the Flood in St John's Church this afternoon, a success by all accounts. After attending Graeme Gibson's event in the Peppers Theatre, she walks across the square to the RBS Main Theatre. The tent is filled with excited people of every age, clutching hardcover copies of the new novel and ancient dog-eared copies of Bodily Harm and The Robber Bride. Clearly she's an author whose work has become a part of many individual histories. I'm somewhere near the back with a radio producer who I've just made friends with in the press pod.

There's a buzz in the tent followed by enthusiastic applause as Atwood walks onto the stage with chair Jenny Brown.

Atwood tells us that she grew up with Victoria novels, which were full of chapters beginning with 'meanwhile'. The Year of the Flood is a parallel story to Atwood's last novel Oryx and Crake, mostly set in the pleeblands, a society which Oryx and Crake's elite protagonist Jimmy views from the window of a sealed bullet train. This is also the shadowy world into which his mother vanishes.

The author didn't plan to write The Year of the Flood while she was writing Oryx and Crake, making her preparation for her new novel a bit laborious. Both novels have a pandemic, post-apocalyptic theme. Atwood reminds us that the SARS epidemic began as she was promoting Oryx and Crake, and was particularly widespread in Toronto, where the author lives. Since then, the world has seen West Nile Virus, Avian Flu and now the Swine Flu pandemic.

Atwood tells us that when writing she considered the early Europeans who went to what are now the Americas, and introduced diseases such as Smallpox to which the population had no immunity, leading to a 100% death rate in some communities. The author asks us to consider the consequences of the invention of a virus to which the world population has no immunity.

On the subject of genre, Atwood tells us that she prefers the name speculative fiction to science fiction. Not because she dislikes science fiction, but because she feels a responsibility not to mislead the reader. The author comes from a family of scientists, who keep her informed on the likelihood her literary inventions. Her brother, apparently, wasn't too keen on the purring function of the new humans in Oryx and Crake. We're told that until Oryx and Crake, the author, who reads scientific journals for fun, didn't invent things for her fiction which hadn't been done before - and her two recent novels feature things which had been done but which weren't widely known, such as the glowing animals.

God's Gardeners, the cult Atwood invents for The Year of the Flood, have all the components of a religion. A set theology, yearly observances, ritual behaviours, a calendar of feasts and saints' days: Saint Al Gore, Saint Jacques Cousteau and Saint Robert Burns of Mice amongst them. God's Gardeners are vegetarians, except when they're really hungry. The use of urban gardening isn't unknown; Atwood tells us it's a growing trend, as is urban beekeeping. The novel employs a long tradition of bee lore. The cult make use of the Bible, though Atwood does not define them as Christians.

The voices of the characters are distinct; from Toby's story in the third person and Ren's story in the first, to the striking difference between the language of the elite and the language used in the pleeblands. The voice of Adam One is thick with religious rhetoric.

Atwood is now a blogger, she tells us dryly. She tweets as well, and does this largely to promote the work of the RSPB which she supports, and who benefit in part from the dramatic readings with musical accompaniment which Atwood developed. The current tour is as green as possible; Atwood carries her own organic shade-grown coffee.

Another confession; I queued to have my copy of The Year of the Flood signed after the event. Then walked back to Leith, listening to The Tragically Hip on my iPod. Another part of the Canadian psyche.