This is the gripping story of the collision between two vastly different human civilisations. One is Earth in the early 21st century, rushing toward self-inflicted nuclear doom. The other is the distant world of Mollan, whose inhabitants have achieved great longevity and the power to transport themselves instantly from star to star.

Bob Shaw's novel unfolds a tale which spans thousands of years and the reaches of interstellar space. On Earth's side, there is Denny Hargate, whose indomitable courage drives him to alter the course of history. On their side is the Gretana ty Iltha, working on Earth as a secret observer, who dreams of returning to the delights of her world's high society, but who gets caught up in a cosmic train of events leading to an explosive climax.