How and when will the Universe end? Gravity and dark matter are poised to annihilate the Universe in a big crunch. Expansion and dark energy may tear it apart. Or, a phase transition could kill us tomorrow in a cosmic death bubble.

The Sea of Cortez, also known as the Gulf of California, is a unique corner of the Pacific Ocean. This remarkable young sea is thought to be around five million years old and home to nearly 900 species of fish and the widest variety of whales and dolphins found anywhere on Earth. Some of the greatest changes threatening the world's oceans today can be seen in this stretch of water.

Brian explores the physics of the size of life through some close encounters with Australia's wildlife. From swimming with great white sharks to tracking red kangaroos, he discovers that the size you are profoundly affects the life you lead and, ultimately, how long you have to enjoy it.

The wartime contributions of five prominent Hollywood film directors during World War II are profiled. The documentary focuses on five directors – John Ford, William Wyler, John Huston, Frank Capra, and George Stevens – whose war-related works are analysed by modern filmmakers, respectively Paul Greengrass, Steven Spielberg, Francis Ford Coppola, Guillermo del Toro, and Lawrence Kasdan. In the first episode, John Ford's The Battle of Midway was approved directly by President Franklin D. Roosevelt while Frank Capra fights to get Why We Fight made.

In the last episode of the series, lavish imperial games at the Colosseum are highlighted by the emperor's bloody victories, but his paranoid abuses of power lead to a final betrayal.

The Southern Ocean, which circles the globe without being blocked by land, is home to the Antarctic Circumpolar Current (ACC), the longest of the world's ocean currents. Also known as the "channel", it connects the Indian, Atlantic and Pacific Ocean basins and exerts a powerful influence over the Earth's climate. The ACC carries 150 times more water around Antarctica than the flow of all the world's rivers combined.