Hauntingly written, this book is both a masterpiece and a masterclass in investigative journalism — Seierstad helpfully even gives notes on the process at the end ... Most of all, this is a portrayal of the effect of the girls’ departure on their family: their eldest brother, Ismael, abandons religion, while their mother returns to her native Somalia, taking her two youngest with her ... The main protagonist is really [the girls' father] Sadiq and his almost Shakespearean descent into despair.

Seierstad structures the book perfectly, with sections examining the sisters' radicalization intertwined with their father's desperate bid to recover them ... She paints a fascinating and even-handed picture of Ayan and Leila's growing fundamentalism, but she doesn't claim to know what exactly caused their conversion ... She also does a deft job of capturing the emotions of the principals in the story — not just the sisters, but also Sadiq, whose life is essentially destroyed by his daughters' journey to ISIS ... Two Sisters is nearly impossible to stop reading. She's a master at pacing, and writes with an admirable clarity that manages to be empathetic without ever descending into mawkishness. And her translator, Seán Kinsella, does a wonderful job making the book accessible to English-language readers ... Two Sisters is a fascinating, heartbreaking, and, finally, urgently necessary book.

In Two Sisters, Norwegian journalist and writer Åsne Seierstad...tries to...turn the fanatical ghosts back into complex humans – by telling in intricate, compelling detail the story of one family dragged into Isis’s web of horror ... In her exploration of how and why Ayan and Leila abandoned their home for a distant war, Seierstad weaves a complex picture of their lives as young Norwegians ... Seierstad also teases out the sense of alienation that a distinct and different heritage can produce in a homogeneous society – Ayan’s exploration of her roots and religion, Leila’s isolation at school ... an unfolding human drama whose characters are compelling – from the strong-willed young women and desperate parents at the story’s heart to the shifting cast that surrounds them – womanising fundamentalists, well-meaning but clueless Norwegian teachers, the loyal Syrian smuggler with close ties to al-Qaida ... There is no update on the whereabouts of Leila or Ayan, giving the reader some sense of the void their parents and siblings stare into every day, wondering what happened to them, the two bright girls from Oslo.

'We were blind. We thought it would pass. Now we know better. ' This admission is tucked away at the very end, in an afterword. It explains the prickling feeling you might have while reading the book that information is being withheld, that Seierstad knows more than she’s telling ... Seierstad is at her best when she pans out to consider the variety of reasons Western women join ISIS (by 2013, there were 3,000 Westerners in Syria, several hundred of them women), drawn by a hunger for sisterhood, adventure and membership in a society they felt was colorblind — where shared allegiances were more important than race ... Extremism more often follows crises in identity and in community, when other narratives of making sense of the self have fallen away. This is what becomes obvious every time the sisters in Seierstad’s book flicker into focus, when their voices can be heard, unmediated. This story of theirs has yet to be told — despite the resonant clues they left along the way — and even as it promises to be repeated by others.

Seierstad delves into the lives of the sisters before they left, as they slowly were drawn into the beliefs of the terrorist group, and examines the crater they left in the lives of their parents and brothers after their departure ... As extreme as their decision was, this incremental retelling of their conversion reveals just how perniciously a powerful doctrine can take over young lives.

Ayan and Leila did not respond to Seierstad’s requests to speak to her for this book ... Even without the sisters’ voices, the passages in which Seierstad attempts to piece together how the girls were radicalized are absorbing ... Seierstad, perhaps still sensitive after the trials of Bookseller, admits in an extensive reporter’s note that she allowed Sadiq and Sara to read Two Sisters before publication. Her deference to Sadiq might be one reason we get few details regarding what he and Sara were like as parents. And although much of the book takes place in Norway, I didn’t emerge with a vivid sense of why the girls rejected it. Seierstad shows the Norwegian teachers struggling with the girls’ lifestyle choices — wearing the niqab in school, leaving in the middle of class for prayers — but she never pulls back and describes Norway in her own words, as if it, too, might be as foreign a place for the reader as the Islamic world ... As monstrous as it was, the Islamic State gave these girls a reason for living. I’m not sure we understand yet why secular societies often do not.

Through well-researched character sketches, Seierstad (who also authored a book on the trial of neo-fascist terrorist Anders Breivik) skilfully brings this dark milieu to life ... Seierstad’s literary journalism is patched together from texts and chats as well as school files and interviews ... What explains the appeal of such savagery? Seierstad deliberately proposes no answer, only the implied lesson, or reminder, that people may become so convinced of their own fictions that they experience vice as virtue and an inferno as paradise.

Two Sisters is a harrowing read, as it lays bare the most barbaric aspects of humanity, taking us into the ISIS camps in Syria where young children are brutalized and made to participate in beheadings, stonings and crucifixions all in the name of pleasing God ... This is a cautionary tale of what can happen when a society moves from simply tolerating antisocial religious beliefs to actually incubating and enabling them.

Hundreds of young people have left Norway to join the Islamic State in Syria, but what gives Two Sisters unusual emotional power is a third character: Ayan and Leila’s father ... Seierstad is good at re-creating a scene, so we are right there when Juma slips across the Turkish border into Syria. Readers can feel the seediness of the local hotels and will find themselves bristling at the sketchy characters who say they will help the desperate father find his girls ... the strongest sections involve the unvarnished look we get into a complicated father-daughter relationship ... If I have issues with the book, they involve Seierstad’s journalistic decisions ... But these are quibbles. Two Sisters provides an immense contribution to our understanding of how the Islamic State is able to persuade so many young people to abandon their comfortable lives in the West to join its cause in Syria.

The story thread here is Sadiq’s attempts to bring the girls home. But Seierstad has told it in the form of living theater and, as such, the book has all the momentum of Thomas the Tank Engine. There are long sections of aimless messaging between Ismael and Leila, and time slows as pieces are moved around the board as in a draw-bound chess match ... Who needs more misery when what Seierstad has delivered is a good dose of raw, slow agony on one hand and raw, unaccounted ecstasy on the other, and, to all appearances, never these two shall meet.

Seierstad’s exhaustive reporting mines original sources, such as texts and other forms of messaging, but she does not include any interviews with Ayan or Leila, neither of whom would grant permission to the author to write about them. The author defends her decision to go forward without consent. 'The entire world is trying to understand the reasons for radicalization among Muslim youth,' she writes.Two Sisters offers readers that understanding without judgment, in a manner only great journalism can accomplish.

The book is more gripping narrative than cultural study, especially in the dramatic scenes of Sadiq’s imprisonment. Seierstad’s scrupulous reporting shines a revealing new light on the phenomenon of young Westerners becoming fervent supporters of terror.

In which the sins of the children are visited upon the fathers: an unblinking journalistic account of the life of the jihadi ... 'Is it ethically defensible to focus on the lives of two girls when they have not granted their consent?' Seierstad wonders at the end. That is for readers to decide, now knowing much more about what drives people to fanatical causes.