Professor Whitrow takes us on a good-humoured and wide-ranging tour of what clocks keep (more or less). He discusses how our ideas of time originated; how far they are inborn in plants and animals; how time has been measured, from sundial and hourglass to the caesium clock; and whether time possesses a begining, a direction, and an end. He examines the differences between cyclic, linear, biological, cosmic, and space-time, and provides frequent diversions into fascinating topics such as the Mayan calendar, the migration of birds, the dances of bees, precognition, and the short, crowded lives of mu-mesons, particles produced by cosmic-ray showers that exist for just two-millionths of a second.