Every society throughout the world - and throughout history - has had a place for music. It has been used in sacred rituals and worship, for celebration and entertainment, for healing, and for protest. This three-part series considers how and why music has developed such an important role. Jeremy Marre filmed phenomena as diverse as the spirit cults of Madagascar, the trance rituals of Bali, the throat-songs of the Inuit Eskimos, flamenco in Cordoba, Wagner in Bayreuth, a therapy group in Ireland, duetting birds in Panama, samba in Brazil and an exorcism in old Cairo for this exploration of the nature of music.