How did Hitler decide he was a messiah and persuade a whole nation to follow him to damnation? This is a subject that has been mined many times in fiction - Raiders Of The Lost Ark, Constantine, Hellboy, Bulletproof Monk and English horror writer James Herbert's book The Spear - as well as documentary. Based on Ken Anderson's 1995 book of the same name, this aims to show how the Nazi party was originally made up of several occult groups that believed a messiah was on the way to save Germany.

Al-Khalili travels to northern Syria to discover how, a thousand years ago, the great astronomer and mathematician Al-Biruni estimated the size of the earth to within a few hundred miles of the correct figure. He discovers how medieval Islamic scholars helped turn the magical and occult practice of alchemy into modern chemistry. In Cairo, he tells the story of the extraordinary physicist Ibn al-Haytham, who helped establish the modern science of optics and proved one of the most fundamental principles in physics - that light travels in straight lines. Prof Al-Khalili argues that these scholars are among the first people to insist that all scientific theories are backed up by careful experimental observation, bringing a rigour to science that didn't really exist before.