The girl is 15 years old but looks much younger. Her face has the fine-boned elegance typical of her native Somalia, but her accent belongs to the streets of East London. She is plainly terrified. That much is clear from the way she avoids eye contact and constantly fidgets in her chair.
"Promise you won't print my name or anything?" she implores repeatedly. "Promise no one will ever know that I've spoken to you? If people in my community find out, they'll say that I've betrayed them and I'll have to run away. And anyway, I don't want my parents to be sent to jail."
With great courage, this British-Somali girl - she asks that we call her "Lali" - is about to describe a barbaric act of ritualised cruelty which has been perpetrated against her. Knowing the danger to which she is exposing herself, her anxiety is entirely understandable.
For by speaking about it, Lali will break the ultimate taboo among Britain's 600,000 ethnic Africans. In Norway, where this brutal act is also prevalent, a young Somali woman was recently beaten, almost to death, for talking to TV documentary programme-makers.
It is known by a variety of names, the most common of which are female genital mutilation (FGM), female circumcision, or simply "cutting" - a word which somehow conveys the raw pain its prepubescent victims suffer.
Most people will be unfamiliar with this practice, which involves removing part or all of the clitoris, the surrounding labia (the outer part of the vagina) and sometimes the sewing up of the vagina, leaving only a small opening for urine and menstrual blood.
It is carried out for a variety of cultural reasons. Such is the secrecy that surrounds the practice that even those aware that it occurs in large swathes of Africa and Asia will be shocked to learn that it is prevalent in Britain.