Among Britain's Somali community there are alarming rumours about the number of young men heading to Somalia to fight with the Islamist militia al-Shabab.
But when we asked to meet someone who has gone or knows someone who has gone, we were met with blank faces.
Then, in a draughty community hall in north London, we were introduced to a young woman - we will call her Amina - with a story to tell.
Amina is Somali-born but international in her outlook. A student in London, she works part time in a fashionable clothes shop and likes to travel the world.
She says her younger brother was much the same, a true Brit who liked his friends and football. But there is a lot about her brother that she does not know.
Last year after graduating from university, the 21-year-old announced he was going to Egypt with his best friend to study religion.
From there, he phoned home and sounded happy but after a few months, his tone changed. "It seemed someone was there with him and every time he tried to say something, they would cut the phone off," she said.
Later, she learned he was in Somalia with al-Shabab, and six weeks ago, she spoke to him for the last time.
He said "make sure mum's OK. I'll find a way to be back". A few days later, his friend rang with news that her brother had been killed by a missile.
The family are devastated and full of questions to which there are no answers. How did he get the money to travel? Who recruited him? Why did he go?
Amina believes that, as well as her brother and his friend, two other friends have gone to Somalia to fight with al-Shabab. British security services believe that scores of young Somalis have done the same. The head of MI5, Jonathan Evans, warned in September that it was only a matter of time before someone trained in insurgency returned to commit an act of terrorism in the UK.
Professor Peter Neumann, director of the International Centre for the Study of Radicalisation at King's College, London, describes al-Shabab as one of the top three al-Qaeda affiliate organisations, and currently the only one that is gaining territory.
In Somalia, wherever the Islamist militia takes control, it imposes a brutal form of Sharia law.
It has also shown its ability to act outside the country too, by carrying out suicide bombings in Kampala, Uganda. 74 football fans who had gathered to watch a screening of this summer's World Cup final were killed by two bomb attacks.
On the streets of London, Birmingham and Sheffield, you will not hear Somalis talking openly about al-Shabab.
Mohammed Abdullahi, director of the UK Somali Community Initiative, says it is only discussed in restaurants or private houses where people know others share their views and they change the subject when someone new walks in.
As a consequence, it is hard to gauge the level of support.
If young people are being radicalised, it is likely to be happening via the internet and chat rooms.
The organisation has a sophisticated propaganda machine, broadcasting images of the destruction in the Somali capital Mogadishu, and portraying its militia as a band of brothers fighting against a puppet government propped up by the West, and against African peacekeepers, described as "crusaders".
In 2007 it broadcast the "martyrdom video" of a suicide bomber called Abdul Ayoub al Muhajir, a British Somali from Ealing in west London who killed himself and 20 Ethiopian soldiers.
In it, he appeals to other British Muslims to migrate to Somalia and wage jihad against their enemies.
Prof Neumann believes that, as long as al-Shabab is confident of success in Somalia, it may not feel motivated to carry out an attack in a Western country.
However, he says the greatest threat comes from the independent operator who returns from Somalia and takes action.
It is a fear echoed by Mohammed Abdullahi, who believes Somalis themselves will suffer most from an attack on British soil. "Our biggest fear is that they get trained and come back and do something here".