This episode is concerned with technology from history that was either ahead of its time and subsequently forgotten, or artefacts which are mysteries in themselves. This includes the Baghdad battery, where German scientist Arne Eggebrecht is shown electroplating a small silver statue with a gold cynanide solution and a replica of the battery using grape juice. There are also segments on the Antikythera Mechanism (including an interview with Derek J. de Solla Price), the Stone Balls of Costa Rica and the so-called 'Skull of Doom' which famously dominates the opening credits of the series.

Clarke opines at the end that had some of these forgotten technologies been developed and not lost that we would have 'colonised the stars' by now.