The year is 1998, the world is a growing nightmare of desperation, of uncontrollable pollution and increasing social unrest. In Cambridge, two scientists experiment with tachyons - subatomic particles that travel faster than the speed of light and, therefore, according to the Theory of Relativity, may move backwards in time. Their plan is to signal a warning to the previous generation.
 
In 1962, a young Californian scientist, Gordon Bernstein, finds his experiments are being spoiled by unknown interference. As he begins to suspect something near the truth it becomes a race against time - the world is collapsing and will only be saved if Gordon can decipher the message in time.
 
Winner of the Nebula Award for best novel, 1980
Winner of the John W. Campbell Award for best novel, 1981
Winner of the BSFA Award for best novel, 1980