At first glance, Jamilla and Ameena couldn't be more different. Both are Yorkshire-born teenage girls of South Asian descent; but whereas Jamilla lives with her conservative Muslim family and is quiet, religious and academically bright, the more worldly Ameena masks her insecurity behind a brassy, bawdy persona and lives with her divorced mum.

The two strike up an unlikely, fateful friendship. Ameena teases Jamilla about her hijab, nicknaming her 'nunja', but also accompanies her to a study group at the mosque as a lark. In the wake of a deeply bruising rejection by a popular boy at school, Ameena develops a serious interest in religion. She begins to espouse a militant version of Islam, and communicates over the Internet with a recruiter for jihad in Syria, influencing Jamilla in turn.

Filled with a new sense of belonging as well as idealised visions of a new spiritual order, the girls flee England for Islamist Syria. Once there, Ameena marries a jihadi she met online. Jamilla, however, resists marriage and becomes a lieutenant to the wife of a powerful commander, whose 'orphanage' turns out jihadi brides and suicide bombers in equal measure.

The girls slowly realise that their new reality is a narrow, brutal universe apart from the one they had imagined. Ameena copes by becoming ever more zealous, and increasingly dangerous to Jamilla. Cornered and desperate, Jamilla must figure out how to save herself from her former best friend…