LONDON • The night before teenager Khadiza Sultana left for Syria, she was dancing in her bedroom.
It was a Monday during the February school vacation. Her niece and close friend, at 13 only three years younger than Khadiza, had come for a sleepover. The two girls wore matching pyjamas and giggled as they gyrated in unison to the beat. Khadiza offered her niece her room and shared a bed with her mother.
She was a devoted daughter, particularly since her father had died.
The scene in her bedroom, saved on the niece's cellphone on Feb 16 and replayed dozens of times by Khadiza's relatives since, shows the girl they thought they knew: joyful, sociable, funny and kind.
It was also the carefully choreographed goodbye of a determined and bright teenager who had spent months planning to leave her home in Bethnal Green, East London, with two schoolmates, to follow another friend who had travelled to territory controlled by the Islamic State in Iraq and Syria (ISIS).
On Tuesday morning, Khadiza said she was picking up some workbooks from school before spending the day in the library. She promised to return by 4.30pm. When she had not come back by 5.30pm, her mother asked her oldest sister, Ms Halima Khanom, to message her, but there was no reply. School staff said no student had come in that day.
Her mother checked her wardrobe and found it mostly empty.
"That's when I started panicking," Ms Khanom, 32, said.
Early the next day, Khadiza's family reported her missing. An hour later, three police officers from the counter-terrorism squad knocked on the door. "We believe your daughter has travelled to Turkey with two of her friends," one said.
The next time Ms Khanom saw her sister was on the news: Grainy security camera footage showed Khadiza and her 15-year-old friends, Shamima Begum and Amira Abase, calmly passing through security at Gatwick Airport for Turkish Airlines Flight 1966 to Istanbul and later boarding a bus to the Syrian border.
These images turned the three Bethnal Green girls, as they have become known, into the face of a troubling phenomenon: young women attracted to what some experts call a militant, girl-power subculture.
An estimated 4,000 Westerners, more than 550 of them women and girls, have joined ISIS, according to the Institute for Strategic Dialogue, which manages a database of female travellers to the region.
The men tend to become fighters. Barred from combat, the women support ISIS state-building efforts as wives, mothers, recruiters and sometimes online cheerleaders of violence. Security officials now say they may present as much of a threat to the West as the men: Less likely to be killed and more likely to lose a spouse in combat, they may try to return home, indoctrinated and embittered.
The three girls were praised by teachers and admired by students at Bethnal Green Academy. Khadiza was singled out as one of the most promising students in her year. Her friend Amira was a star athlete.
Perhaps that is why many signals were missed: The families, who noticed the girls' behaviour changing, attributed it to teenage whims; school staff, who saw their homework deteriorate, failed to inform the parents or intervene; police, who spoke to the girls twice about the friend who had travelled to Syria, also never notified the parents.
In post-9/11 austerity Britain, as a crisis of identity and values has swept the country, fitting in can be harder for Muslim girls than for boys. Buffeted by a growing hostility towards Islam, they have come to resent the Western freedoms and opportunities their parents sought out. They see Western fashions sexualising young girls.
Going to Syria and joining ISIS is a way of "taking control of your destiny", said lawyer Tasnime Akunjee, who represents the girls' families.
In January last year, one of Khadiza's friends, Sharmeena Begum, lost her mother to cancer. Her father started courting a woman who would become his second wife.
Sharmeena, deeply shaken, started praying and spending more time at the mosque. Khadiza accompanied Sharmeena to her father's second wedding. Soon after, Sharmeena disappeared. Khadiza and her friends began planning to follow.
Ms Khanom made contact with Khadiza via her Instagram account, weeks after she left. She sent Khadiza a private message, asking to let her know that she was safe.
"I'll call soon okay," Khadiza said.
Ms Khanom pleaded with her to return, saying that the police said the girls would not be prosecuted.
"They're lying," Khadiza replied.
All three girls have since married, their families' lawyer confirmed.
They say they have few regrets about leaving their lives in London, but hint at hardships like electricity cuts and shortages of Western goods. One recent chat ended because air strikes were starting.
Increasingly their words are interspersed with propaganda phrases.
"Have they adapted that language, or is there someone standing next to them?" Mr Akunjee asked. "We don't know."
NEW YORK TIMES