Elinor, aged about 30, toils on the innermost planet Mercury, exploited as a vast mine of metals and minerals. This is a life of enslavement, of hard physical labour. But now she has a baby son, Alfa. Alfa will be physically strong, but also shows signs of high intelligence - and so he may be selected to be taken to Saturn, where is to be found the highest technology in the Solar System - and a decent life.
But as it turns out labourers are going to be in more demand when Alfa is ready to start work, aged about seven. Elinor can't stand the idea of a life like hers for her baby son - and so she cuts off his right hand, rendering him of no use for manual labour.
The Solar System is as it is because, in the 25th century, the Scavengers, alien resource-hunters, arrived in the outer System and demolished Neptune, outermost of the major planets. Then it was discovered that the comet cloud beyond the planets is the rubble of an earlier predation, made before humans could observe and understand. If they have come twice, there is a danger that the Scavengers will return again to pick off more planets - eventually, Earth.
And as he grows Alfa comes to suspect that Fortress Sol is built on lies inside as well as outside . . .
