In this authored historical investigation, historian Tom Holland traces the origins of Isis's extreme violence, which it claims is justified by the tenets and scriptures of Islam. Travelling from Paris to Istanbul, and from Sinjar to Cairo, he examines the roots of Isis's interpretation of notions such as jihad and caliphate; he investigates why Isis have persecuted different religious minorities in different ways; and he asks whether the group's ideology is in part a reaction to a westernisation of Islam that ultimately dates back to the time of Napoleon. Holland questions the assertion - much repeated by western leaders - that Isis has nothing to do with Islam. He examines the origins of the group's beliefs, which he traces back to the very origins of Islam.