The only person in the world who could have enticed 15,000 children to a baseball stadium to hear someone read from a book finally arrived in Canada last week. British writer Joanne Kathleen Rowling, creator of the hugely popular Harry Potter series, came to Toronto and Vancouver to meet her fans, to attend a fund-raising lunch for children's literature, to headline the largest literary reading ever staged, and - - not incidentally -- to renew an extraordinary friendship that began with a letter she received in July, 1999.

At the time, Harry-mania was already exploding in English-speaking countries. In Edinburgh, Rowling was hunkered down, refusing all media requests and most outside distractions, as she worked feverishly on the lengthy story that eventually became the 636-page Harry Potter and the Goblet of Fire. And in Toronto, nine-year-old Natalie McDonald was dying. "She was obsessed with the Harry Potter books," remembers family friend and political activist Annie Kidder. "They had been her respite from the hell of leukemia. And because I'm the sort of person who thinks there must be something I can do, I badgered Rowling's publishers in London, sending them a letter and an e-mail and a fax for her."

Passed on by the publishers, the letter arrived at Rowling's Edinburgh home a day after the author had left for a holiday in Spain. "When I came back two weeks later and read it, I had a bad feeling I was too late," Rowling told Maclean's. "I tried to phone Annie but she wasn't in, so I e-mailed both Natalie and her mother, Valerie -- because Annie hadn't told Valerie what she had done." Rowling was right in her foreboding -- the e-mails were received the day after Natalie died on Aug. 3.

"Jo's e-mail was beautiful," Kidder says. "She didn't patronize Natalie, or tell her everything was OK; she addressed her as a human being who was going through a hard time. She talked about her books and her characters and which ones she liked best." And most remarkably of all, Rowling freely shared the secrets of her fourth novel, details media and fans desperately sought for another 11 months.

The story might have ended there, but Valerie McDonald wrote back, in thanks. "That letter touched deep," Rowling says slowly, trying to explain the esteem in which she holds Natalie's mother. "I just knew, reading it, that if we had been two mothers waiting for our kids at the school gate we'd have been friends." So a regular correspondence began, and an unexpected friendship -- "the one moment of light in this whole horrible thing," says Kidder -- was cemented last summer when McDonald, her husband, Bruce Stratton, and their two daughters travelled to Britain to meet Rowling. But even before that, the author had quietly commemorated the reader she never met. On page 159 of Goblet of Fire, the famous sorting hat of Hogwarts School of Witchcraft and Wizardry sends first-year student Natalie McDonald -- the only real person named in any of Rowling's novels -- to Harry's own Gryffindor house. It was during that English visit last summer, reading the just-released Goblet of Fire to her daughters while riding on the London tube, that Valerie McDonald learned of Rowling's gesture. And on Rowling's first day in Canada, says the writer, she spent a "wonderful" afternoon at Niagara Falls with the McDonald family and Kidder.

The public part of Rowling's visit went very well, too, to put it mildly. When she arrived in Toronto on Oct. 22, the writer said she was nervous about reading from her novel before thousands of children in the city's cavernous SkyDome. Two days later at the stadium podium, Rowling evidently still felt the same way, responding to a thunderous cheer with "I'm delighted -- and terrified -- to be here." But as soon as she spoke, 15,000 children dropped into a rapt silence they hadn't quite managed for the two popular Canadian authors -- Ken Oppel and Tim Wynne-Jones -- who read before her. And when Rowling finished 14 minutes later, the children erupted in loud and sustained applause. Accompanying adults might have grumbled about the acoustics, but the kids were happy to be there. Nine-year-old Iain McCann had to make a hard choice to miss taking part in Toronto's cross-country running championships in order to attend, but he wasn't complaining: "It'll be a memory for the rest of my life, like a historical date."

Rowling's incredible sales -- some 40 million copies worldwide -- have left commentators struggling to explain her success. Praise for the absorbing Potter novels is near universal, but good stories alone do not seem explanation enough. A truer answer may lie in Rowling's interaction with children as seen on her current tour and in the manner of her letter to Natalie McDonald. The writer's jam-packed six-day visit to Canada had its share of inevitable, adult-world glitches. (Besides the SkyDome's execrable sound quality there was Rowling's address at the fund-raising lunch, so unexpectedly brief that the next speaker had to scramble to get up on stage.) But with children Rowling unfailingly connects.

The best part of her book tours is "meeting child readers," she told reporters. "They ask the best questions -- no offence to any of you. The children talk about the characters as though they're mutual friends I happen to know a bit better." And despite large "no autographs" signs at the fund-raising lunch for the Toronto Public Library's Osborne Collection of Early Children's Books, a steady stream of children successfully approached her throughout. "Poor Jo," sighed Jackie Davis, one of her security staff, "she never gets to eat lunch."

Respect for children, who Rowling thinks are "grossly underestimated" by most adults, is also apparent throughout the Potter novels. Death is a major theme. The villain wants to live forever, by whatever means it takes, and the hero is the child of murdered parents, whose mother died to preserve his life. Death and family are inextricably linked for Rowling. "I'm fascinated with big families in the stories I like, probably because I'm from such a small one," she says. "My parents were so young when they married -- my mother was only 20 when she had me, 23 for my sister, Di -- that we had four living grandparents and lots of great aunts and uncles. But they soon began to die, including my mother from multiple sclerosis when I was 25, so now there's only me, my sister, my daughter, Jessica, my father and one aunt."

Perhaps it's Rowling's family history that has given her the "handle on dying" that Toronto bookseller Jessy Kahn, owner of The Constant Reader, sees in her books. "She deals with death very sensitively. I didn't think of it until customers began to return for additional Harry Potter copies to give to friends who had suffered a loss. And those people found them comforting." A pleased Rowling responds: "If that's the case, then I'm very gratified." She sounded surprised by Kahn's remarks. Valerie McDonald probably wouldn't be.