he Sun has gone out and the Earth is lit only by the glow of residual vulcanism. The last few millions of the human race are gathered together in the Last Redoubt, a gigantic metal pyramid, nearly eight miles high, which is under siege from unknown forces and Powers outside in the dark. These are held back by a shield known as the "air clog", powered from a subterranean energy source called the "Earth Current". For thousands of years vast living shapes known as the Watchers have waited in the darkness near the pyramid. It is thought that they are waiting for the inevitable time when the Circle's power finally weakens and dies. Other living things have been seen in the darkness, some of unknown origins, and others that may once have been human. Hodgson uses the term "Abhuman" to name several different species of intelligent beings evolved from humans who interbred with alien species or adapted to changed environmental conditions, and are seen as decayed or maligned by those living inside the Last Redoubt.