The Chinese cult that kills 'demons'
The cult in question is called the Church of the Almighty God and claims to have millions of members.
It was an ordinary evening in a small town McDonald's in east China until a family of six arrived trying to recruit new members to their Christian cult.
They moved between the tables asking for phone numbers and when one diner refused they beat her to death, screaming at other diners to keep away or they would face the same fate.
The savage murder was filmed on closed circuit TV and on mobile phones.
It shocked China. Who were these people prepared to kill over a telephone number?
Interviewed in prison later, one of the murderers, Zhang Lidong, showed no remorse and no fear.
He said: "I beat her with all my might and stamped on her too. She was a demon. We had to destroy her."
Fighting 'the big red dragon' The public face of the Church of the Almighty God is a website full of uplifting hymns and homilies. But its core belief is that God has returned to earth as a Chinese woman to wreak the apocalypse.
The only person who claims direct contact with this god is a former physics teacher, Zhao Weishan, who founded the cult 25 years ago and has since fled to the United States.
No one knows exactly where he is, but much of the website's message of outright hostility to the Chinese government is delivered in English as well as Chinese.
It states: "Since the Communist Party came to power in 1949, religious faith has suffered from full-scale crackdown and persecution by the Communist Party - the red dragon - in mainland China."
Of course it's true that until the late 1970s, Communist China did persecute all religious faith, and even now allows it only within strict guidelines.
There are in fact tens of millions of Chinese Christians whose faith is orthodox but who practice it in illegal underground or "house" churches to escape government interference.
But while complaining of Communist persecution, there's no mention on the Church of the Almighty God website of the murders, mutilations, stabbings and riots that some of its own members have been accused of.
Instead it claims millions of followers and says nearly 400,000 have been arrested in the past three years alone.
Resisting the Communist Party, "the big red dragon", is a key test of fitness for salvation according to the personal testaments on the website.
One states: "Even if they beat me to death my soul is still in God's hands. God's word's made my faith firm... I'll never yield to the devil."
A very different picture emerges from those who have lost family to the cult.
Most don't want to reveal their identity for fear of retribution. We talked to one man who went undercover to rescue his wife and father-in-law.
He said: "The cult is anti-family, anti-human, anti-government. It is constantly training its members to lie to their husbands and wives. They throw away family relationships and encourage each other to do the same."
"Whoever is more resolute in rejecting their family is given a higher rank. It takes people who are kind and makes them crazy and extreme."
We found many victims through family support websites and heard of a shadowy cell structure where false names and identities make it almost impossible to trace relatives.
A picture emerged of recruiters who start by offering support and move on to intimidation, who persuade new members to hand over money in exchange for salvation, and who sometimes resort to seduction and kidnapping.
'Heresies and cults' Outside a government-sanctioned church in Beijing's university district, there are large black signboards warning congregations to be wary of cult recruiters.
Christianity provides a sense of shared values and community at a time when the Communist Party seems to many Chinese to have stopped trying.
But the cult promises an even closer-knit community and even more direct route to salvation. Its recruiters are skilled at targeting people at times of vulnerability: a major illness in the family, a marriage break up, a job loss.
Already the government-backed church suffers from a steady flow of Christians to the underground churches.
But the cults recruit much more aggressively and Pastor Wu Weiqing said it's hard to hold onto his flock.
He said: "I very seriously believe in the next 10 years the most serious challenge to the growth of the church would be from heresies and cults."
"The cults and the heresies will always have the opportunities to get those people, get their heart and drag them away from us. "
In an east China cemetery on a hill above vineyards and orchards, Wang Jiannan picks his way carefully between the headstones.
He lost his mother and his sister to the cult nearly 20 years ago. But now he's lost his father too.
On 1 October last year, his sister beat their father to death in a grim forerunner of the McDonald's killing. Like those killers, she saw her victim as a demon who must be destroyed.
She then handed herself into police and is now in prison alongside the McDonald's murderers.
"My sister has committed the crime and must be punished. But I just want my mother to see clearly the damage the cult has done to her family," said Mr Wang.
"I want her to leave and become a normal person. This is my biggest hope."
Since the McDonald's murder, public outrage has forced the authorities to increase the pressure on the Church of the Almighty God.
Recent weeks have seen an almost daily drip feed of raids and arrests.
But so far the cult has inflicted its damage on individuals and families. Despite its vocal hostility to the Communist Party, it has mobilised no meaningful political threat.
And a threat to the Party, rather than the people, is what it takes to trigger a crackdown in China.