In 1928 the physicist Paul Dirac predicted the existence of antimatter in a mirror world, where the electrical charges on particles would be opposite to those of ordinary matter. This mirror world is found, fleetingly, at the quantum level, with positrons the counterpart of electrons, and antiprotons the opposite of protons. This book introduces the world of antimatter without using technical language or equations. The author shows how the quest for symmetry in physics slowly revealed the properties of antimatter. When large particle accelerators came on line, the antimatter debris of collisions provided new clues on its properties. This is a fast-paced and lucid account of how science fiction became fact.