Spy in the Huddle use innovative techniques to reveal the incredible secrets of your pets' behaviour in ways never seen before. As astonishing photography explores the wild side of our playful pets, find out why hamsters love to run in a wheel, how dogs pick up the rules of the pack and how kittens learn to be solitary hunters. Featuring incredible views of plunge-diving dogs, babysitting cats, acrobatic hamsters and a playful cat outwitted by his prey" - you'll never look at your favourite companions in quite the same way again. The latest science also reveals why budgies talk, how a cat scales a vertical wall with the help of a special claw, why hamsters stuff their faces with more food than they can eat and the real meaning behind a rabbit's hop. Our pets are also given a chance to explore their wild side as we join the free-roaming pet dogs of Cusco Peru, pet rabbits living in a natural warren and the wild-living inhabitants of Cat Island, Japan. A range of innovative techniques such as moving X-rays, thermal imagery, minicam-carrying dogs and revelatory slow-motion photography shows why our pets play and how their true wild nature is just a whisker away.

Soldiers and officers continually came into conflict with their consciences. How much freedom did individuals have? Were they executing Hitler's criminal plans, or was it the Wehrmacht's war? There were crimes against humanity, against civilians, prisoners of war, and there was the Holocaust itself. The Trent Park records discovered and analysed by historian Sönke Neitzel, author of Tapping Hitler's Generals, show that the 84 German generals who were interned at Trent Park were aware of the severity of the war crimes they had been involved in and that some discussed them almost compulsively. They included the Commissar Order, to kill any Soviet commissar, and Rathenau's order to kill the Jews, including children.

At 4.6 billion years old, the Solar System is our solid, secure home in the Universe. But how did it come to be? In this episode we trace the system's birth from a thin cloud of dust and gas. Shocked by a nearby supernova, the pull of gravity and natural rotation spun it into a flat disc from which the Sun and planets coalesced. It all happened in the space of 700 million years, during which the planets jockeyed for position, dodging the Late Heavy Bombardment of deadly asteroids and setting into the neat, stable system that we now realize might be a rarity in the universe.

Andrew Graham-Dixon reveals how the Medici family transformed Florence through sculpture, painting and architecture and created a world where masterpieces fetch millions today. Without the money and patronage of the Medici we might never have heard of artists such as Donatello, Michelangelo or Botticelli, and Graham-Dixon examines how a family of shadowy, corrupt businessmen, driven by greed and ambition, became the financial engine behind the Italian Renaissance.

Dark energy - the mysterious force that is unexpectedly causing the universe's expansion to speed up. The effects of dark energy were discovered in 1998 but physicists still don't know what it is. Worse, its very existence calls into question Albert Einstein's general theory of relativity - the cornerstone of modern physics. The hunt for the identity of dark energy is on". Experiments on earth and in space generate data that might provide a clue, but there are also hopes that another Einstein might emerge - someone who can write a new theory explaining the mystery of the dark energy.

The final episode of the series visits the frontline of the conflict with the world's top predators, meeting the scientists fighting to save them. Crossing five continents and combining landmark natural history footage with real-life human drama, it checks the pulse of the earth's iconic animals, including lions, tigers, polar bears and blue whales. With three-quarters of the planet's carnivores now in decline, can people find ways to live with predators before they disappear forever?