A planet manned by robots - three human beings captured and carried off from Earth to that planet: this is the theme of Paul Capon's latest science thriller for young people.

When young Stephen Craig came over from America to stay with his girl friend Daney and her father, all seemed set for a peaceful, happy holiday on the coast, with Mr. Salgado painting landscapes, Daney and Steve swimming and boating. Their weirdest dreams would have seemed tame beside the reality of what befell these three when, while swimming one morning, they were snatched out of the sea by a mechanical monster and transported by it through space.

Phobos is one of the moons which revolve round Mars - so the astronomers say. In Paul Capon's story he tells us that it is really an artificial satellite set going by the Martians - a gigantic mechanical brain which controls the automatons it reproduces.

To this nightmare world the three humans were taken, a world peopled by creatures which could perform superhuman tasks, but could not feel any emotion. What hope of understanding or pity could there be from them? How could Mr. Salgado, Stephen and Daney escape with their lives?

Paul Capon tells the story of their dangers and eventual triumph with that mixture of the factual and the bizarre which make his stories so vivid. However exotic the fantasy it always has its roots in scientific possibilities.