Bored housewife Ella feels stalled despite her gracious suburban life in Northampton, New England. Her teenage children are growing away from her; her husband is distant and unfaithful. Ella's new job as reader for a publisher introduces her to Sufism through a manuscript she is sent to read, and has life-changing consequences.

"Sweet Blasphemy", the novel she is sent to appraise, tells the story of a 13th-century wandering Persian Sufi Dervish, Shams of Tabriz, and his inspirational relationship with Rumi, the greatest poet of the Sufi canon. Rumi, a respected Koranic scholar, was transformed through his love for Shams and was inspired to write the Masnavi, a key Sufi tract which weaves Koranic analysis with poetry, parables of the everyday, the mythic and miraculous. It was to beget Mevlevi Sufism, practised through poetry, music and dance.

The Forty Rules of Love takes Sufism into blockbuster territory. It interweaves Ella's quest to find love with Shams's and Rumi's quest for beatitude through friendship, as told by a range of characters including Rumi's wife and sons: one of whom was to assassinate Shams, the other to carry on his father's work. The narrative is racy, told in first-person fragments, letters, emails and braided through with Shams's theosophy as told through his 40 rules of love. Elif Shafak expounds a populist rather than a scholarly Sufism, providing a vigourous and easily assimilable introduction to Sufi thought.

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Bold bestseller this may be, but there is attention to detail. Each chapter begins with the letter "b". For Sufi mystics the secret of the Koran lies in the verse Al-Fatiha, the essence of which is contained in the word bismilahirahmanirahim (in the name of Allah, the Benevolent and Merciful), with the quintessence of the word in the dot below the first Arabic letter, a dot that embodies the universe. Shams espouses multiple readings of the Koran, and Shafak slips in two diametrically opposed contemporary translations of the Al-Nisa, the Koranic verse which M H Shakir interprets as justification for male subjugation of women - while Ahmed Ali translates as a verse extolling respect for women.

Both the observant head-scarfed daughters of AKP, the Islamic party in government in Turkey, and the secular offspring of past Kemalist regimes, are ardent fans of Shafak's novel. Her engaging vision of a gentle non-judgmental Sufi path to Islam that rejects religious fundamentalism and is accessible to all, from medieval drunks and whores to 21st-century Scottish drifters and American housewives, has made the novel a Turkish bestseller.

Challenging truisms of the fundamentalist Islamic orient and the consumerist Judeo-Christian occident, the novel proposes Sufism as a quest for spirituality which can fill the void at the heart of both. Shafak is a mercurial and often controversial writer, but should she choose to continue in this spiritual vein, I have no doubt she will challenge Paulo Coelho's dominance. With its timely, thought-provoking, feel-good message, The Forty Rules of Love deserves to be a global publishing phenomenon.