The title of Ava DuVernay's extraordinary and galvanizing documentary refers to the 13th Amendment to the Constitution, which reads 'Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States.' The progression from that second qualifying clause to the horrors of mass criminalization and the sprawling American prison industry is laid out by DuVernay with bracing lucidity. With a potent mixture of archival footage and testimony from a dazzling array of activists, politicians, historians, and formerly incarcerated women and men, DuVernay creates a work of grand historical synthesis.

It's this moment where now both sides realize that no quarter will be asked, and no quarter will be given. Surrender is no longer even an option. You're in this to the end. You either die or you triumph, and there is no other alternative. Amid a spiral of brutality and low morale, Mehmed makes Giustiniani an enticing offer. The grand vizier urges Mehmed to seek a truce with his rival.

Is mankind alone, or are there aliens out there, either waiting to be discovered, or on their way to find Earth? Professor Brian Cox spends this episode asking such questions, and what he discovers may raise a few eyebrows. He begins by exploring the human race's efforts to find neighbours in outer space, including the launch of two golden discs containing a greeting from Earth in the 1970s; they are still travelling and are now the most distant man-made objects from the planet. Brian also meets members of the Search for Extra-Terrestrial Intelligence, who have been monitoring radio signals for 50 years without success, before discussing the ingredients needed to make an intelligent civilisation with astrophysicist Dr Frank Drake.

Vlad Dracula presses an increasingly desperate guerrilla campaign from the shadows, hoping to demoralize the Ottomans and slow their march north. After chasing Vlad for two weeks, sultan Mehmed II and his invading army find themselves caught in a nightmare come to life deep within the Wallachian forest. Many legends have arisen out of the invasion of Wallachia in 1462. One speaks of Vlad Dracula launching a biological attack against the Ottomans to slow their march to his capital city, Târgovişte. Vlad opened his prisons and released hardened criminals to go amongst the Ottomans with tuberculosis and bubonic plague so that they could infect the enemies.
Vlad Dracula also had carried out a scorched-earth policy against Mehmed II. Along with his hit-and-run campaign from the shadows has left the sultan's troops on edge. As Mehmed's army closes on Târgovişte, tensions flare in the Ottoman camp, where food and water are in increasingly short supply. But Vlad had nowhere to rely on food for himself either and there was nowhere to go anymore. He became a prisoner of his own scorched-earth policy. Radu Dracula closes in to take Princess Anastasia hostage. Anastasia commits suicide when he reach her at Poenari castle.

After more than a century of civil war, Toyotomi Hideyoshi has united Japan. His rivals have either sworn their allegiance, or they have been destroyed. Despite this fledgling peace, Hideyoshi now dreams of a bold and outlandish plan to make himself the most powerful man in Asia. He plans to expand his reign to China. Logistical challenges and fierce operation in Korea prove to be costly.

The Cave of Swallows in Mexico is a 400m vertical shaft, deep enough to engulf the Empire State Building. The Lechuguilla cave system in the USA is 193km long and 500m deep with astonishing crystal formations hanging from its chambers. Although often overlooked, caves are remarkable habitats with equally bizarre wildlife. Cave angel fish cling to the walls behind cave waterfalls with microscopic hooks on their flattened fins. Cave swiftlets navigate by echo-location and build nests out of saliva. The Texas cave salamander has neither eyes nor pigment. Unique access to a hidden world of stalactites, stalagmites, snotites and troglodytes brings a wealth of surprises.