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.

In the second episode, Nathan develops a rehearsal for Angela, a woman considering motherhood. Nathan hires child actors to simulate adopting and caring for a baby and sets her up in a rented farmhouse in rural Oregon. Due to Oregon child protection laws, Nathan's team must covertly switch out the baby every four hours and replace it with a robot baby at night. Seeking a simulated husband, Angela dates Robbin, a numerology-obsessed man who wants to have sex with Angela despite her devout Christian beliefs against premarital sex. When Robbin quits the project due to the robot baby's incessant crying, Nathan inserts himself into the experiment as Angela's non-romantic co-parent.

Electricity is not just something that creates heat and light, it connects the world through networks and broadcasting. After centuries of man's experiments with electricity, the final episode tells the story of how a new age of real understanding dawned - how we discovered electric fields and electromagnetic waves. Today we can hardly imagine life without electricity - it defines our era. As our understanding of it has increased so has our reliance upon it, and today we are on the brink of a new breakthrough, because if we can understand the secret of electrical superconductivity, we could once again transform the world.

Lucy Worsley continues her journey through Russia in the footsteps of the Romanovs, the most powerful royal dynasty in modern European history. In this episode she examines the extraordinary reign of Catherine the Great, and the traumatic conflict with napoleonic France that provides the setting for the novel War and Peace. At the magnificent palace of Peterhof near St Petersburg, Lucy charts the meteoric rise of Catherine the Great, who seized the Russian throne from her husband Peter III in 1762 and became the most powerful woman in the world. Catherine was a woman of huge passions - for art, for her adopted country (she was German by birth) and for her many lovers.
Catherine expanded her empire through military victories overseas, while at home she encouraged education and introduced smallpox inoculation to Russia. But Catherine struggled to introduce deeper reforms, and the institution of serfdom remained largely unchanged. Lucy explains how this injustice fuelled a violent rebellion. Nevertheless, Catherine left Russia more powerful on the world stage than ever. But all she had achieved looked set to be undone when Napoleon invaded Russia in 1812. Lucy relives the pivotal battle of Borodino, when the Russian army finally confronted the French forces; the traumatic destruction of Moscow; and, under Catherine's grandson Alexander, the eventual victory over the French that provided the Romanov dynasty with its most glorious hour.

Caesar winters his army in Gaul near the Italian border while his enemies in Rome fear that he will do something no Roman General has done: cross the Rubicon with his army. To counter-balance his opponents, Caesar puts his friend Mark Antony up for office as the people's Consul. Vorenus and Pullo accompany Mark Antony and Octavian to Rome. For Pullo, it's an opportunity to get drunk and ravish every woman in sight.

Pompey wants to find out what happened to the gold from the Roman Treasury and sends his son Quintus to Rome to find out what happened. Atia and her family have stayed behind when Pompey and others fled and she now throws a party for her triumphant uncle, Julius Caesar. She clearly has her sights set on the great leader and is puzzled when he sends her a guest list that includes Servilia of the Junii. She soon finds out why.