They're mostly young, educated and middle class - yet more than 60 British women and girls have chosen to move to Syria and live in the so called "Islamic State", under a deeply repressive regime. So, according to Foreign Minister Julie Bishop, have a number of Australian women. This BBC investigation reveals how the women marry fighters, and become part of a powerful army of online recruiters, persuading other young girls on social media to join them and about 500 other Western women thought to be living in the self-declared caliphate.