For a woman of 61, who has spent the past five years preparing for, and executing, a variety of taxing global missions (in 2002 she completed 49 days' fasting and sun-gazing in Newfoundland), Bai looked well. She is a strong, smiling woman with competent hands with which she likes to rub people's backs as a relaxing greeting. She was dressed completely in white, and when we took our seats she prudently put on a white jacket in preparation for the abrupt climate shift with which every cinema-goer in Hong Kong is familiar. The film began, the temperature dropped and climactic mayhem ensued on screen. Now and then Bai leaned forward, gazing in disbelief at wolves padding around frigid Manhattan, tornadoes ripping up the hillside Hollywood sign and the two young stars kissing, a point at which the Island School pupils enthusiastically clapped - and Edna patted her on the back, consolingly. (Afterwards, Edna said Bai was a little surprised by what she'd seen because she'd thought the film was going to be a documentary.)

Because the scriptwriter had attributed the Earth's problems to a warming of the north Atlantic current I thought Bai might feel an urge to switch her energies from the sky to the seas, but when we emerged, half frozen, and went to thaw out over coffee, she said her inner voice had now told her to focus on another five-year cycle like the one she has just completed. 'She thought that her five years, and three expeditions, would have completed the mission,' explained Edna. 'But the message is that things are getting worse.'

Bai, eating the coffee shop's biscuits, sighed, no doubt thinking of deprivations to come in the many days after tomorrow. 'She abides by the voice,' said Edna. Bai has been listening to the dictates of this voice since she was volleyball player-turned-coach Yu Shuk-man, living in 1980s Beijing. It instructed her to go on a fast for seven days, after which she became Bai, healer. The voice encouraged her to move to Hong Kong in April 1993, which she did, leaving her retired volleyball coach husband behind.

On March 5, 1994, Bai felt an internal compulsion to wear red, place three red dots on her name card and open a healing clinic in Wan Chai, with all of which she complied. She wore red for a year, was then spiritually instructed to wear yellow for four years, and is now in her white phase; when she goes on her missions, however, she wears a multi-hued, distinctive garment that covers her face, apart from her eyes, and is of a style an Islamic Druid might wear if compelled to gaze at the sun for seven hours at a stretch.

This outfit has caused Bai some problems; not in southern Chile, in December 2000, where the locals of Punta Arenas welcomed her, nor 18 months later, in Newfoundland, in June 2002, where, despite the language barrier, she made many friends, but, I'm sorry to report, in Hong Kong at the end of last year. Bai's missions are 18 months apart and she had intended to travel to the Tibetan plateau for her third outing but, funds being in short supply, Tuen Mun, where she lives with her daughter, seemed the easier option. (I was impressed by the speed with which her global plans, like the climate, could shift, but Edna explained that because Tibet and Tuen Mun are in the same time zone, the physical location wasn't the priority.)

Unfortunately, a group of women at Bai's local temple in Tuen Mun objected to her fashion sense, or, as Edna put it, 'They complained to the police about her costume and kicked her out.' Bai said mildly that she had been saddened by this approach in her own neighbourhood but had completed her first seven days in another area, behind her flat ('Full of dogs honking about and mosquitoes,' said Edna), and had then travelled to the Gold Coast for the following 42 days to complete the ritual. Now she is planning a return trip to Chile next May. When I asked Bai what, if anything, she felt she had achieved so far, she replied, 'If I didn't do it, it would be so much more disastrous. I've driven myself as much as I can to maintain this level.'

Strangely enough, when I searched the internet for information on the state of the ozone layer, it revealed a piece published in The Guardian last August that stated its destruction had significantly slowed. The writer had narrow-mindedly attributed this to the eventual implementation of the 1987 Montreal Protocol banning CFCs, but Bai, said Edna, had another explanation: 'She says it's her love for humanity and her love for the Earth which is helping. This is why her voice tells her the mission must continue.'