Antonie van Leeuwenhoek was a Dutch cloth merchant with no scientific training who built his own microscopes and discovered bacteria, protozoa, and spermatozoa. He was the first person in history to see the invisible world teeming inside a drop of water.

This episode tells the story of how a self-taught tradesman from Delft outperformed the professional scientists of the Royal Society and opened the door to microbiology.

• How he ground lenses capable of 270x magnification by hand
• His discovery of bacteria, which he called animalcules
• The letters to the Royal Society that changed biology
• Why he refused to share his lens-making techniques with anyone