"Elpowa" Industries - the mammoth electro-engineering combine controlling half the galaxy, discovered the Threshold... a scientific gateway to the fourth dimension. The industry and culture of a thousand planets would be revolutionised by that discovery. It would mean the end of orthodox space transport... vast fortunes were at stake... and a galactic war was in progress.

Who were the spacemen trying to sabotage the "Elpowa" process? Who were the Others, with their weird, super-human powers? Where did they come from, and what did they want? How could space liners, and even whole cities disappear without trace?