Any documentary maker knows the oh-my-God moment - when they become aware of an event too valuable to go unfilmed that no one is shooting.

That happened last year when Toronto-based director Ron Mann, 52, ( Comic Book Confidential, Know Your Mushrooms) was talking to Margaret Atwood. The occasion was a meeting about another filmmaker's doc on saving elephants, and how Atwood and Mann might be able to lend a hand to promote the film and its cause, Mann says. Atwood mentioned to him that she was one week away from leaving for Edinburgh to begin what was to become a widely attended, highly unusual book tour.

Instead of the usual readings and book signings for her novel The Year of the Flood, set in a dystopian future of environmental devastation, Atwood wanted to change things up and turn her appearances into theatrical events highlighting environmental awareness. She invited different amateur theatre groups and choirs in each city to perform in churches and small theatres.

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But when Mann asked if anyone was recording this, Atwood said, "No." Amazed, he scrambled to get a film crew together in Edinburgh.

Once the performance was shot, Mann thought it was the end of that little exercise. But then Atwood called to tell him about a subsequent London appearance being put together by renowned film producer Rosa Bosch. Well-known names in the arts were coming out to lend a hand with her environmentally minded, grassroots tour. Again, Mann asked if anyone was filming the event. "No," Atwood said once again.

So when the tour shifted to Canada - where Kingston director Jim Garrard, founder of Toronto's Theatre Passe Muraille and a friend of Mann's, got involved with Atwood's Ontario stop - Mann realized he had to commit. He decided to follow the tour - which eventually took him across the country, to New York, and, eventually, to a new documentary, In The Wake of the Flood. It opens the 11th annual Planet In Focus international environmental film and video festival in Toronto on Wednesday, and is, in a sense, continuing the book tour as the film weaves its way through the festival circuit.

"For me, what was important was the amplification of Margaret's message," Mann says, "the message being both our immediate environmental crisis and a hope of turning things around."

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Hope is a word Atwood herself stresses in the documentary. "The interesting thing about hope," she says with characteristic dryness during a question-and-answer session with an audience in the film, "is that if you don't have any hope, then there's less hope. It is a self-generating thing." On the flip side, she adds, optimism only breeds hope and possibility.

The performances shown in the film often revolve around readings by actors performing scenes from Atwood's book, including one about a notorious (fictional) fast-food chain Secret Burgers, where the mysterious contents of the meat includes offal that's truly awful. Choirs also sing the hymns of the back-to-nature sect in the novel known as God's Gardeners, set to music by Atwood's long-time friend Orville Stoeber.

On her Canadian stops, Atwood is also particularly interested in local issues: She visits a community vegetable garden, she sends Tweets on hazards to migratory birds while taking the train with her publicist to Toronto, and she talks about the specific bird and fish life that has returned to Sudbury, Ont., after that city's environmental devastation at the hands of mining companies half a century ago.

"This is what's so extraordinary about her: She is really a politically active person," Mann says. "[But]she's someone who is really quiet about it. I mean, she is very vocal as a member of PEN [the international writers' group devoted to free speech] But she's also on picket lines. Her whole life has been involved with social-justice movements and environmental movements."

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She does this with a blend of intellect and slight self-deprecation. At one point in the film, she thanks the performers on her tour almost apologetically for taking part in such an unusual event. At another stop, she insists with a smile that the entire audience raise hands and pledge to drink only shade-grown coffee (that is, coffee grown underneath trees, which doesn't involve cutting down bird habitats).

Atwood also let Mann's camera into her Toronto house and writing room, showing a rare, more intimate glimpse of the novelist. We see her tending to her lush Toronto garden and walking through her tastefully appointed home. Even more fascinating for her fans are the glimpses of the author in her large writing room. With her desk by the window and stacks of books in the far corner, the space is very sunny, inviting and airy, not at all hermetic. It looks like the room of someone at peace with herself, her writing and her environmental work.

"There's a certain kind of fatigue with environmentalism, where it's all about how depressing it is. But what Margaret represents for me is hope, that we can all actually do little things to have an impact. That's the difference between the 1960s and today: It's not what you're against; it's what you're for," Mann says.

For detailed screening information, visit planetinfocus.org.