Talk to Germans of Turkish descent and many recall childhood friends who gravitated towards religious conservatism and, having donned headscarves and more modest customs, slowly and quietly drifted away. "Gulen", they say, and shrug.

They're referring to the religious movement of the US-based Turkish Sunni cleric Fetullah Gulen, built around the notion of Hizmet, or "service", which runs hundreds of educational establishments across the world, spanning from Afghanistan to Tanzania and the United States.

It's a secretive movement which originated in Turkey, whose structures remain largely opaque and who members are unwilling to profess their adherence to Gulen. This has resulted in criticism that the movement lacks transparency and has an agenda of indoctrination and Islamization through its network of schools and free tuition centres.

In Germany, the movement was long a darling of politicians, given its focus on free education among the German-Turkish community, nurturing bright students and helping them access higher education and high-level jobs.

Expert: no grand master plan

But in recent years, it has received more scrutiny, not least after its long-time alley, Turkish President Recep Erdogan, publicly split with the group, accusing it of infiltrating state institutions and even outright "terrorism".

Germany's intelligence services disagree: In 2014, they published an assessment outlining that while some elements within the movement gave room for concern, such as statements made by Gulen which "conflicted with core principles of the democratic order", they didn't warrant an observation of the movement.

Kristina Dohrn, a cheerful, outgoing anthropologist, who has been studying the movement for almost ten years in Germany and Africa, pauses for a second when asked to characterize the movement: "It's a global, conservative network with a strong focus on education", she finally says. "But you could also call it a kind of work ethic."

Members, who meet in weekly prayer sessions and study the teachings of Gulen, are expected to "find jobs which are good for the community" - and for many that means serving the wider community through education: Many become teachers, and are sent to the movement's many schools and free tuition centres across the globe, "which are supposed to raise the religious elites of tomorrow, which are then expected to move into positions of power."

And yet, Dohrn is convinced that there is no grand master plan to take over and Islamize the world: "At the most, there's a shared vision of an 'ideal' society, but it's one that remains vague."

Inside a light-house

The group's elites of tomorrow, the bright students who are expected to work hard and progress into important positions in society, often live in so-called "light-houses", shared flats, strictly separated by gender and financially supported by the Gulen movement.

In the past, the Gulen movement was wary of giving media access to such flats, which host weekly seminars and study meetings. But today, thousands of its members - both actual and suspected - are being rounded up and imprisoned in Turkey among accusations that they were conspiring to take over the country in a failed coup attempt earlier this year.

As the conflict quickly spread outside Turkey, dividing the Turkish community in Germany into camps supporting either Erdogan or Gulen, DW has been finally allowed access to one of the five light-houses in Berlin, which houses female students.

Outside the nondescript block of flats in central Berlin, a family of five scurried home, as the boom of a premature New Year's Eve firecrackers reverberated through the narrow street.  Inside the tidy flat, a polite, eloquent young woman with a light-blue headscarf and long tunic, who DW agreed to call Özlem, made a pot of ginger tea, while on the table a tiny Christmas carrousel of angels and shepherds danced around a flickering candle.

Split in Turkish community

Özlem is a Gulen supporter who defies the conspiracy theories surrounding the group. She is a young, educated woman with a degree in linguistics who plans to work in educational policy. She also doesn't shy from criticizing the movement she joined when she was fourteen, after an uncle introduced her mother to the movement. Men rather than women, she conceded, often held important positions, and she was quick to condemn the anti-Semitic remarks Gulen made in his earlier writings.

When she moved to Berlin from a small town in rural Bavaria, joining a lighthouse seemed a logical step for Özlem. She calls the five women who share immaculate rooms, books and copies of the quoran neatly stacked on desks, as well as daily prayer meetings, her "surrogate family".

She is, she says, a conservative Muslim, who prays five times a day and is opposed to sex before marriage. But some of her views, she concedes, may clash with those of the wider movement and indeed other light-houses, particularly more conservative Turkish leaders: For one, she's not opposed to gay marriage. It should, Özlem, who says that many of her friends are atheists and Jews, says, be left to the individuals in a secular system, and politics and religions should be separated.

No one, she said, had ever instructed her to take on a certain profession or join a political party.

As a flatmate wandered in to the small kitchen to make dinner, Özlem shook her head. Life, she said, had become difficult for Gulen supporters in Germany. Some mosques have banned known Gulen supporters, labeling them "traitors" and many of her friends now attend mosques in neighbourhoods where no one knows about their secret affiliation. 

But worst of all, the rift has spilt into her family, too: "My father's not religious, and he told us to leave that ‘terrorist network'." Özlem and her four siblings refused and, after several heated rows, the family reached a shaky truce: "At home, we simply don't talk about Gulen and politics any more."

But, she said, her father still jokes that his children are "terrorists". She shrugged.