The tentacles of intense, evangelised belief have reached into scores of families across Europe. The young – inspired, excited and, above all, committed – have headed into a hellish conflict, leaving everything behind. The cauldron of violence in the Middle East has lured in not only the typical young men desiring action, but also a cohort of young women, intent on embracing a radically different way of life, baffling their family and friends with confident asseverations that ‘death is better than life’.

When this phenomenon is reported in many European countries, including our own, there is usually a lack of illuminating detail and domestic circumstance. The shocked families curl up with grief and fear, and eventually the media interest tails off. Here is one of those stories, but it is meticulously documented, full of drama, with phone calls from the very centre of ISIS terror, jokey emails home, parents at their wits’ end and desperate journeys into a warzone.

Asne Seierstad, a formidable Norwegian investigative journalist, follows every significant moment in the lives of Sara and Sadiq Juma, who, one night in 2013, were faced with an empty bedroom and the inexplicable absence of their daughters. A Somali couple with five children, based near Oslo, they believed they were some way towards achieving a new life, living carefully and frugally, and expecting much from their children’s embrace of a sophisticated education system.

In the immediate aftermath of the girls’ disappearance, modern communication intervenes, connecting the family in Norway with the teenagers on the move towards Syria. Ayan and Leila have mobile phones. They live on the net. They call, email, chat and sound like normal teenagers rabbiting on – except that their comments are littered with religious statements, their actions justified with copious quotations from Islamic texts. They express no doubts and no regrets, leaving their parents desperately asking, ‘How did this happen?’

While still in shock, Sadiq decides on an unusual course of action. Days after the girls’ disappearance, he flies to Turkey and travels south to the border with Syria, willing to chance his luck with the murderous ISIS machine. What is usually a vague picture of the route to the chaotic theatre of war here becomes vivid, filled with smuggling, violence, ever-changing loyalties and tension.

Seierstad’s meticulous research reveals a complex and compelling picture of the gradual radicalisation of two independent-minded, modern, cool girls. The charismatic young Islamic imams in Norway play their part. There is the daily issue of ‘How do I dress?’ Headscarf? Niqab? Teachers remember thoughtful discussions. The state makes decisions on dress codes in schools. The girls take to covering up more and more, but officials can’t decide whether it’s typical teenage rebellion or pressure from the more traditional elements in the Somali community. Meanwhile their parents cannot find their way through the puzzle of being both Somali and Norwegian.

The religious gatherings, the political protests, the establishment of contacts with radicalised fighters, the change in dress: all happen in plain view. Yet Sadiq and Sara are still stunned by what has happened to their daughters. As they head further into the ISIS heartlands, the girls pop up on Facebook, Viber and Skype; they text and call. They’re heading for marriage and babies. They seem near-oblivious of the torture and execution that happen daily in their new society. Their chatter is most likely being monitored by men upholding the harshness and rigidity of the Islamist cause. Even so, after more than two years, the girls, both of them now mothers, assert confidently that ‘we need to make more babies – if the war is a long one, we need to make more soldiers.’ They luxuriate in the free housing, washing machines and SIM cards provided by ISIS. They answer questions with Koranic quotes.

It’s a credible and all too common story of our times. Seierstad presents us with the divisions and dilemmas that we would like to follow with reason and sympathy. Vast numbers of people now find themselves in a culture different from that of their upbringing, where, despite attempts at integration, the sheer force of primitive fundamentalism blasts and burns through the delicate connections that hold together both societies and families.

This is a tale fluently told, and a thriller as well, about two young girls who left Norway one evening and were last heard of in the city of Raqqa.