Between the microscopic world of quarks and atoms, and the macroscopic one of pebbles, planets, and galaxies there is another world, strangely neglected by science since Isaac Newton. It is inhabited by pollen, DNA and viruses, not to mention globules of paint, shampoo, milk and chocolate. Smaller than molecules but bigger than atoms, its tiny denizens have one thing in common: they cannot keep still. Physicist Mark Haw tells the story of the discovery of this restless middle world 200 years ago; how it was ignored for so long, and how it spectacularly answered Einstein's most basic question about the nature of matter in the twentieth century. Despite this, science ignored it again until very recently. Haw reveals that today, understanding the weird, jiggling "mesoscale" has become central to nanotechnology, medicine and working out the origins of life.