At the beginning of 2015, three London schoolgirls travelled to Syria to join Islamic State. The oldest was only sixteen, and all three were described in the hundreds of newspaper reports as ‘straight-A students’ from apparently happy families. They weren’t alone; in 2015, at least 56 women from the UK made the same journey, and the pattern was similar across Europe and beyond.

Morgan Jones by James Alexander

Morgan Jones by James Alexander

Men had signed up in greater numbers, but the women’s individual stories were somehow more shocking. Unlike so many of the men, they weren’t petty criminals, didn’t have mental health problems, hadn’t struggled with addiction. The girls from Bethnal Green were like our daughters, our wives, our friends - they were like us. And they forced us to ask a distressing question: what was wrong with our society that three happy, bright young women should choose to embrace all that violence and terror? Or were they simply devils?

The question fascinated me because it touched on so much: faith, education, multiculturalism, the recent history of the west and the middle east. But in particular it seemed to shine a light on the growing sense that everywhere and in different ways young people were rejecting the world their parents had shaped for them. I have two teenage children, and for every opportunity my generation has created I see two deep problems it will take other generations to solve.

I began to read as many first-hand sources from inside ISIS as I could - blogs, twitter accounts, the oddly candid records of these women’s lives - and unbidden a voice began to settle in my head: clever but naive, full of righteous anger, desperate to find some meaning in life beyond the naked commercialism it saw all around. Pushed by honest impulses but without the judgement to predict where they might lead. Smart enough to identify the problem but too passionate to understand that certain solutions would be so much worse. A very teenage voice, in fact.

In The Good Sister this belongs to Sofia, who narrates half the book. I wrote her narrative first, driven forward by her developing character as she was driven to Syria by her convictions, and in the process found myself drawn into territory I wasn’t expecting to explore and conclusions I wasn’t expecting to reach. This alien creature who seemed so hard and unknowable began to reveal herself as something altogether more human, and more vulnerable.

I’ve lost the quotation, but someone once said that one of the things a novel can usefully do is to try to find sympathy for a monster - a character who repels us all for good reason. That is Sofia, who does terrible things herself and condones far worse in others. The world condemns her, but her father, without a clear idea of his intentions and acting on faith and love alone, follows her to Raqqa. At once disgusted, disbelieving and full of a natural fear that he is responsible, he does his best to move towards some kind of understanding - and in the process, I hope, takes us with him at least some of the way.

The story is set in September 2014, eight months after ISIS occupied Raqqa, at a time when its momentum was at its peak and hundreds of fighters a month were travelling to join up. Four years on, the organisation is finished as a territorial power, and the book is in part a historical document. But the aftermath of the whole episode is still playing out: last month an 18-year would-be ISIS recruit became one of the youngest women to be convicted of terrorism offences in this country; in Iraq the trials of hundreds of female members of ISIS are being conducted swiftly, decisively, and without mercy. The mechanisms that drew these women into the organisation still work, and the world that they rejected has barely changed. What took women like Sofia to Syria still has a terrible currency.

The Good Sister by Morgan Jones is published by Mantle.