Boko Haram's appetite for exemplary violence and kidnapping women and girls has thrust it to the top of the global news agenda. In a few furious years its cadres have all but severed parts of northern Nigeria -- Africa's most populous state and largest economy -- from the hands of the government in Abuja. Videos broadcast by Boko Haram feature its leader, a grimacing rantingdemagogue who taunts viewers, claiming he will 'eat the heart of the infidel' and calling on Nigerians to reject their corrupt democracy and return to a 'pure' form of Islam. Thousands have been slaughtered in their campaign of purification which has evolved through a bloody civil war. In Northern Nigeria - which has witnessed many caliphates in the past - radical ideas flourish and strange sects are common. Boko Haram has drawn on and exploited these traditions to mobilise people against the corruption of Nigeria's politicians and oligarchs who have preyed on a state buoyed by oil revenues and turned public institutions into spoons for the pot. When the going was good it didn't matter. Now a new ravenous force threatens them all. Andrew Walker guides the reader through Boko Haram's hinterland - examining northern Nigeria's history, culture and politics - in search of where the group comes from and where Nigeria might be going.