Nader al-Mutairi stiffened his shoulders, clenched his fists and said: “Let’s do our mission.” Then the young man stepped into the cool, empty lobby of a dental clinic, intent on getting the phone number of one of the young women working as a receptionist.

Asking a woman for her number can cause a young man anxiety anywhere. But in Saudi Arabia getting caught with an unrelated woman can mean arrest, a possible flogging and dishonour, the worst penalty of all in a society where preserving a family’s reputation depends on faithful adherence to a strict code of separation between the sexes.

Above all, Nader feared that his cousin Enad al-Mutairi would find out he was breaking the rules. Nader is engaged to Enad’s 17-year-old sister, Sarah. “Please don’t talk to Enad about this,” he said. “He will kill me.”

The sun was already low as Nader entered the clinic. Almost instantly, his resolve faded. His shoulders drooped, his hands unclenched and his voice began to quiver. “I am not lucky today; let’s leave,” he said.

It was a flash of rebellion, almost instantly quelled. In the West, youth is typically a time to challenge authority. But what stood out in dozens of interviews with young men and women in Saudi Arabia was how completely they have accepted the religious and cultural demands of the Muslim world’s most conservative society. They chafe against the rules, even at times try to evade them, but they can be merciless in their condemnation of those who flout them too brazenly. And they are committed to perpetuating the rules with their own children.

That suggests that Saudi Arabia’s strict interpretation of Islam, largely uncontested at home by the next generation and spread abroad by Saudi money in a time of religious revival, will increasingly shape how Muslims around the world will live their faith. Young men like Nader and Enad are taught that they are the guardians of the family’s reputation, expected to shield their female relatives from shame and avoid dishonouring their families by their own behaviour. It is a classic example of how the Saudis have melded their faith with their desert tribal traditions.

“One of the most important Arab traditions is honour,” Enad said. “If my sister goes in the street and someone assaults her, she won’t be able to protect herself. The nature of men is that men are more rational. Women are not rational. With one or two or three words, a man can get what he wants from a woman. If I call someone and a girl answers, I have to apologise. It is a violation of the house.”

Enad is the alpha male, a 20-year-old police officer with an explosive temper and a fondness for teasing. Nader, 22, is soft-spoken, with a gentle smile and an inclination to follow rather than lead.

They are more than cousins; they are lifelong friends and confidants. That is often the case in Saudi Arabia, where families are frequently large and insular.

They are average young Saudi men, residents of the nation’s conservative heartland, Riyadh, a flat, clean city of 5m that gleams with oil wealth, two glass skyscrapers and roads clogged with oversized SUVs. It offers young men very little in the way of entertainment, with no movie theatres and few sports facilities. If they are unmarried, they cannot even enter the malls where women shop.

Nader sank deep into a cushioned chair in a hotel cafe, sipping fresh orange juice, fiddling with his cellphone. If there is one accessory that allows a bit of self-expression for Saudi men, it is their cellphones. Nader’s is filled with pictures of pretty women taken from the internet, tight face shots of singers and actresses. His ringtone is a love song in Arabic. “I’m very romantic,” Nader said. “I don’t like action movies. I like romance. Titanic is No 1. I like Head Over Heels. Romance is love.”

Three days later, in a nearby restaurant, Nader and Enad were concentrating on eating with utensils, feeling a bit awkward since they normally eat with their right hands.

Suddenly the young men stopped focusing on their food. A woman had entered the restaurant alone. She was completely draped in a black abaya, her face covered by a black veil, her hair and ears covered by a black cloth pulled tight. “Look at the Batman,” Nader said derisively, snickering.

Enad pretended to toss his burning cigarette at the woman, who by now had been seated at a table. The glaring young men unnerved her. “She is alone, without a man,” Enad said, explaining why they were disgusted, not just with her but with her male relatives, too, wherever they were. “Thank God our women are at home,” Enad said.

Nader and Enad pray five times a day, often stopping whatever they are doing to traipse off with their cousins to the nearest mosque. Prayer is mandatory in the kingdom and the religious police force all shops to shut during prayer times. But it is also casual, as routine for Nader and Enad as taking a coffee break.

To Nader and Enad, prayer is essential. In Enad’s view, jihad is too, not the more moderate approach which emphasises doing good deeds, but the idea of picking up a weapon and fighting in places like Iraq and Afghanistan.

“Jihad is not a crime, it is a duty,” Enad said in casual conversation. “If someone comes into your house, will you stand there or will you fight them?” He was leaning forward, his short, thick hands resting on his knees: “Arab or Muslim lands are like one house.”

The concept is such a fundamental principle, so embedded in their psyches, that they do not see any conflict between their belief in armed jihad and their work as security agents of the state. As a police officer, Enad helps to conduct raids on suspected terrorist hideouts. Nader works in the military as a communications officer.

Each earns about 4,000 riyals a month, about £500, not nearly enough to become independent from their parents. But that is not a huge concern, because fathers are expected to provide for even their grown children, to ensure that they have a place to live and the means to get married. To many parents, providing money is seen as more central to their honour than ensuring that their children get an education.

Each young man has the requisite moustache and goatee and most of the time dresses in a traditional robe. Nader prefers the white thobe, an ankle-length gown; Enad prefers beige.

But at weekends they opt for the wild and crazy guy look, often wearing running pants, tight short-sleeved shirts, bright colours, stripes and plaids together, lots of Velcro and elastic on their shoes.

There are eight other children in the house where Enad lives with his father, his mother and his father’s second wife. The apartment has little furniture, with nothing on the walls. The men and boys gather in a living room off the main hall, sitting on soiled beige wall-to-wall carpeting, watching a television propped up on a crooked cabinet. The women have a similar living room, nearly identical, behind closed doors.

The house remains a haven for Enad and his cousins, who often spend their free time sleeping, watching Oprah with subtitles on television, drinking cardamom coffee and sweet tea – and smoking.

Enad and Nader were always close, but their relationship changed when Nader and Sarah became engaged. Enad’s father agreed to let Nader marry one of his four daughters. Nader picked Sarah, although she is not the oldest, in part, he said, because he actually saw her face when she was a child and recalled that she was pretty.

They quickly signed a wedding contract, making them legally married, but by tradition they do not consider themselves so until the wedding party, set for this spring. During the intervening months they are not allowed to see each other or spend any time together.

Nader said he expected to see his new wife for the first time after their wedding ceremony – which would also be segregated by sex – when they are photographed as husband and wife.

“If you want to know what your wife looks like, look at her brother,” Nader said in defending the practice of marrying someone he had seen only once, briefly, as a child. That is the traditional Nader, who at times conflicts with the romantic Nader.

Soon his cellphone beeped, signalling a text message. Nader blushed, stuck his tongue out and turned slightly away to read the message, which came from “My Love”. He sneaks secret phone calls and messages with Sarah. When she calls, or writes a message, his phone flashes “My Love” over two interlocked red hearts. “I have a connection,” he said quietly as he read, explaining how Sarah manages to communicate with him.

His connection is Enad, who secretly slipped Sarah a cellphone that Nader had bought for her. These conversations are taboo and could cause a dispute between the two families. So their talks were clandestine, like sneaking out for a date after the parents go to bed.

Enad keeps the secret but it adds to an underlying tension between the two, as Nader tries to develop his own identity as a future head of household, as a man. Enad teases Nader, at one point saying: “In a year you will find my sister with a moustache and him in the kitchen.”

“Not true,” Nader said, mustering as much defiance as he could. “I am a man.”

Another flashpoint: the honeymoon. Nader is planning to take Sarah to Malaysia and Enad wants to go. He suggests that Nader owes him. “Yes, take me,” Enad says, with a touch of mischief in his voice.

Nader cannot seem to tell if he is kidding. “You know, he can be crazy,” Nader said. “He’s always angry. No, he is not coming. It is not a good idea.”

Nader grew up in Riyadh and his parents, like Enad’s, are first cousins. Enad says his way of thinking was forged in the village of Najkh, 350 miles west of Riyadh, where he lived until he was 14 with his grandfather. It is where he still feels most comfortable.

When he can, he has a cousin drive him to his grandfather’s home, a one-storey concrete box in the desert, four miles from the nearest house. There is a walled-in yard of sand with piles of wood used to heat the house in the cold desert winters.

Inside there is no furniture, just a few cushions on the floor and a prayer rug. Enad is quiet and hides his cigarettes when his grandfather comes through. He would never tell his father or grandfather that he smokes and remains stone-faced when a cousin mentions that another of his cousins, a woman named al-Atti, 22, is interested in him. The topic came up because another cousin, Raed, had asked al-Atti to marry him and she refused.

The conflict and flirtation touched on so many issues – manhood, love, family relations – that it sparked a flurry of whispering and even Enad was drawn in.

Al-Atti had let her sisters know that she liked Enad, but made it clear that she could never admit that publicly. So she asked a sister to spread the word from cousin to cousin and ultimately to Enad. “It’s forbidden to announce your love. It is impossible,” she said.

Word finally reached Enad, who tried to stay cool but was clearly interested and flattered. At this point Enad was himself whispering about al-Atti, trying to figure out a way to communicate with her without actually talking to her himself. He asked a female visitor to arrange a call and then pass along a message of interest.

Enad said it was never his idea to pursue her but that a man –a real man – could not reject a woman who wanted him. To get his cousin Raed out of the picture, he suggested that al-Atti’s brother take Raed to hear al-Atti’s refusal in person, at her house. “From behind a wall,” Enad said.

“Love is dangerous,” al-Atti said as she sat with her sisters in the house. “It can ruin your reputation.”

© New York Times News Service 2008

Times recommends

• The pink mile: women on death row
• The top 10 richest streets in the world
• Japan's new professional seducers