Opus Dei, a mysterious arm of the Catholic Church, has come under the spotlight after the new education secretary in the UK government, Ruth Kelly, revealed she receives spiritual guidance from it, and the best-selling novel the Da Vinci Code placed it at the centre of an international plot for control of the Vatican. So what is known about the group?
Society is fascinated by secretive religious organisations because they allow us to imagine the worst about what murky deeds happen behind their barred doors. The abusive activities of some cults have proved worse than anyone feared, but other times the reality is disappointingly banal.
One "cult" in ancient Rome was widely known to practice child-sacrifice, cannibalism and incestuous orgies during its initiates-only "Love Feasts." That's the cult we know today as the Christian church. There can be smoke without a fire.
So what is the reality behind the rumours about Opus Dei, the Catholic movement that has been awarded its first British parish; that Education Secretary Ruth Kelly says she gets spiritual support from, and that was unflatteringly depicted in The Da Vinci Code?
It has been repeatedly accused of cult-style manipulation, encouraging physical self-harm and having historical links with General Franco's fascist rule in Spain. Critics call it misogynistic, fundamentalist, and opposed to modern society.
Opus Dei denies the "cult" tag", saying it is a forward-thinking arm of the Catholic Church which is "flourishing in the modern world". If it were involved in cult-style practices, it says the Catholic Church would suppress it. It also denies any fascist links. It admits, however, that "mistakes" have been made in the past.
Opus Dei was formed in 1928 in Madrid by the priest Josemaria Escriva de Balaguer. Its name means "the work of God". The fundamental idea was to encourage Catholic lay people to see religion as something that should direct every minute of their lives, rather than being a matter of just turning up for Mass and confession. Members are expected to live holy lives, evangelise people they know, and observe daily religious devotions.
In other words, Opus Dei demands a kind of monastic commitment, except that, in Escriva's words, disciples are "immersed in the blood-stream of society." "It does not take anyone out of his place," he said.
The spirituality of the movement is based on Escriva's book The Way, a collection of 999 meditations to help prayer. He was canonised by Pope John Paul II in 2002. The organisation is estimated to have between 80,000 and 90,000 members in 80 countries, and a reported 500 in the UK.
Opus Dei teaches that even the minutiae of life should be pleasing to God, from doing one's job well to being cheerful, from right beliefs to good manners. It puts a lot of emphasis on serving God through work. It encourages prayer, Bible-reading and Mass every day. Thus far, it is fairly orthodox Christian teaching.
Members have weekly "fraternity talks" with their superiors, discussing the successes, failures and targets of their spiritual lives - self-denial, "the apostolate" (trying to win others to Opus Dei), and sexual temptations. This is one area that opponents criticise, saying it can be manipulative and invasive, and makes unreasonable demands.
Certainly "spiritual direction" is not unique to Opus Dei, but critics say there are obvious dangers in a closed environment.
Opus Dei says these fraternal chats work in the same way as any spiritual guidance given in any Catholic organisation. Members are free to pick and choose what to discuss and what advice, if any, to take.
Since 1982, an internal statute has stated that new members must be aged 18 or over, although children can apply to join at 16-and-a-half.
Another criticism from former members is that they have been forbidden from reading all kinds of books - even many on the reading list at their Catholic University.
Opus Dei says members ask for advice before reading a book, and they are free to reject it.
"Even the Pope asks for advice about what to read, as he explains in his latest book," says Jack Valero, Opus Dei's UK spokesman.
Advanced members - "numeraries" - are celibate, and agree to donate whatever earnings they don't need for basics such as food and housing to the organisation. Many who have left report that they had to pay their entire income to Opus Dei.
Reports that numeraries must have their mail vetted by superiors are dismissed by the group, which says this was customary in the past but was stopped some years ago.
Official Opus Dei literature maintains, "In their political, financial or cultural activities, they act with freedom and personal responsibility, not attempting to involve the Church or Opus Dei in their decisions."
The practice that is most hair-raising for outsiders is "corporal mortification". Numeraries are given a spiked garter to wear round the thigh for two hours a day, and a whip for their own back or bottom. These exercises, explains the Opus Dei constitution, are "for the purpose of chastising the body and reducing it to servitude". Members are also encouraged to take cold showers every day and spend several hours in silence. In the words of Escriva's The Way, "Blessed be pain. Loved be pain."
Opus Dei claims this is merely an example of Christian "self denial" although critics believe it goes beyond that.
In fairness, much of this alleged domination and self-punishment - though not the subterfuge - has been standard aspects of monasticism for 1,700 years. Whether Opus Dei uses them in a healthy and ethical way, and whether monastic tradition justifies anything anyway, is the source of much of the current controversy about the group.