In the third part of his journey into the history of Christianity, Professor Diarmaid MacCulloch charts Orthodoxy's extraordinary fight for survival. After its glory days in the eastern Roman Empire, it stood right in the path of Muslim expansion, suffered betrayal by crusading Catholics, was seized by the Russian tsars and faced near-extinction under Soviet communism. MacCulloch visits the greatest collection of early icons in the Sinai desert, a surviving relic of the iconoclastic crisis in Istanbul and Ivan the Terrible's cathedral in Moscow to discover the secret of Orthodoxy's endurance.

Dr. Thomas Asbridge explains how in the thirteenth century, after almost two hundred years of Holy Wars, the titanic conflict between Christianity and Islam, known to history as The Crusades, reached a decisive and shocking conclusion – a chapter that despite its drama has been virtually forgotten. He explains how, in the end, the fate of the Holy Land was decided not on the hallowed ground of Jerusalem, but in Egypt; and how the ultimate outcome of the Crusades was dictated not by Christians, but by the Mongol successors to Genghis Khan, and by a Muslim slave – a fearsome warrior whose story is now all but lost to western history.

We all project images of ourselves online - a curated identity that defines how we want to be perceived. But what temptations exist to embellish and what are the dark implications? In this episode, enter the world of Cyberbanging, where inner city youth are using social media to brag, conspire and incite violence; two African-American women bloggers who have turned the table on the trolls who threaten them; and the creator of Abdullah X, an online character who's trying to keep Muslim kids from falling under the spell of Islamic extremists.

Investigative journalist Jeremy Scahill travels to Afghanistan, Yemen, Somalia, and other countries where the United States has taken military action in the War on Terror. In Afghanistan, he investigates the United States military and government cover-up of the deaths of five civilians, including two pregnant women killed by US soldiers from the Joint Special Operations Command. After investigating the attack, Scahill travels to other sites of JSOC intervention, interviewing both proponents and opponents, and the survivors, of such raids,including U.S. Senator Ron Wyden. Scahill also investigates the assassinations of American citizens Anwar al-Awlaki and his son Abdulrahman al-Awlaki, meeting with their family at their home in Yemen. Scahill suggests that the War on Terror is in fact a "self-fulfilling prophecy" and causes the radicalization of Muslims. He also discusses the case of Yemeni investigative journalist Abdulelah Haider Shaye who was detained, tried and sentenced on terrorism-related charges after reporting on American drone strikes.

Michael Wood charts the coming of Islam to the subcontinent and one of the greatest ages of world civilisation: the Mughals. He visits Sufi shrines in Old Delhi, desert fortresses in Rajasthan and the cities of Lahore and Agra, where he offers a new theory on the design of the Taj Mahal. He also looks at the life of Akbar, a Muslim emperor who decreed that no one religion could hold the ultimate truth, but whose dream of unity ended in civil war.

The Queen of Sheba - an exotic and mysterious woman of power - is immortalised in the world's great religious works, among them the Hebrew Bible and the Muslim Koran. She also appears in Turkish and Persian painting, in Kabbalistic treatises, and in medieval Christian mystical works, where she is viewed as the embodiment of Divine Wisdom and a foreteller of the cult of the Holy Cross. In Africa and Arabia her tale is still told to this day and, indeed, her tale has been told and retold in many lands for nearly 3,000 years.