Between the 8th and 14th centuries, scholars across the Islamic world built on Greek and Persian learning to lay groundwork for modern optics, chemistry, medicine, and mathematics, and physicist Jim Al-Khalili travels to the places where that work happened. In Syria he traces the marketplaces and study houses where knowledge moved between cultures; in Iran he examines the work of Ibn Sina, whose medical writing shaped both Islamic and European practice for centuries. Tunisia's Kairouan gets a stop for Ibn Khaldun's early social theory, and Cordoba, in Andalusian Spain, anchors a look at the library built under Al-Hakam II, once one of the largest collections of books in the world. Along the way the film credits Ibn al-Haytham's experiments with light and vision, al-Razi's work in chemistry, Al-Khwarizmi's algebra, Al-Battani's astronomical observations, and Al-Zahrawi's surgical instruments and techniques. Al-Khalili narrates from each location, using the buildings and manuscripts themselves as evidence for how translation and exchange between cultures carried this science forward.