Just 92 elements made up the world, but the belief that were only four - earth, fire, air and water - persisted until the 19th Century. Professor Al-Khalili retraces the footsteps of the alchemists who first began to question the notion of the elements in their search for the secret of everlasting life.He reveals the red herrings and rivalries which dogged scientific progress, and explores how new approaches to splitting matter brought us both remarkable elements and the new science of chemistry.

In part two, Professor Al-Khalili looks at the 19th century chemists who struggled to impose an order on the apparently random world of the elements. From working out how many there were to discovering their unique relationships with each other, the early scientists' bid to decode the hidden order of the elements was driven by false starts and bitter disputes. But ultimately the quest would lead to one of chemistry's most beautiful intellectual creations - the periodic table.

In this episode, Michael demonstrates how our society is built on our search to find the answer to what makes up everything in the material world. This is a story that moves from the secret labs of the alchemists and their search for gold by the stone of the philosophers to the creation of the world's first synthetic dye - Purple - and onto the invention of the transistor. This quest may seem abstract and highly theoretical. Yet it has delivered the greatest impact on humanity. By trying to answer this question, scientists have created theories from elements to atoms, and the strange concepts of quantum physics that underpin our modern, technological world.

The documentary 'The Knowledge of Healing' is an illuminating examination of Tibetan medicine, a practice which has developed over two millennia into a modern day successful method of healing that rivals western medical practices. Unlike Western medicine, based on biochemistry, Tibetan medical thinking (which is strongly rooted in Buddhist principles) views the human body as governed by an elaborately organized system of energies flowing through a network of channels. In the 12th century, the Gyüshi (Knowledge of Healing) was created, a text codifying this intricate system. The medications used comprise herbs, roots, minerals, etc. After flourishing for centuries, most Tibetan medical schools were destroyed by the Chinese in the 1950's and 1960's, and many physicians were executed. Speaking from exile, the Dalai Lama argues for the value of Tibetan medicine, while his personal physician Dr. Tenzin Choedrak describes the principles behind it. We follow physicians in India and Siberia treating patients for a variety of ailments from paralysis to heart disease, and meet researchers in Israel and Switzerland to see how western clinical studies are testing the effectiveness of Tibetan medicine.

Sagan discusses the story of the Heike crab and artificial selection of crabs resembling samurai warriors, as an opening into a larger discussion of evolution through natural selection (and the pitfalls of intelligent design). Among the topics are the development of life on the Cosmic Calendar and the Cambrian explosion; the function of DNA in growth; genetic replication, repairs, and mutation; the common biochemistry of terrestrial organisms; the creation of the molecules of life in the Miller-Urey experiment; and speculation on alien life (such as life in Jupiter's clouds). In the Cosmos Update ten years later, Sagan remarks on RNA also controlling chemical reactions and reproducing itself and the different roles of comets (potentially carrying organic molecules or causing the Cretaceous–Paleogene extinction event).

In the final part, Professor Al-Khalili uncovers tales of success and heartache in the story of chemists' battle to control and combine the elements, and build our modern world. He reveals the dramatic breakthroughs which harnessed their might to release almost unimaginable power, and he journeys to the centre of modern day alchemy, where scientists are attempting to command the extreme forces of nature and create brand new elements.