See also my reviews of Salt, Stone and Polystom

Adam Roberts' first novel, Salt, which came out last year, was a very fine start to any career. On is only his second novel and raised two important questions for me: one, will his titles continue to shorten (perhaps his third novel will be the chemical name for hydrogen or some such)? And two, would Salt prove to have been a mere flash in the pan?

Regarding question two the answer is a cautious 'no' - Roberts looks set to become a regular member of the sf canon, for On is an unusual and thought-provoking novel initially reminiscent of Christopher Priest's Inverted World.

The pristine white cover shows a boy looking cautiously across a desert landscape towards an insect-like craft floating in the air; however it is only upon looking around to the back cover that the true perspective of this picture is revealed: that the boy is looking down a steep cliff - On accomplishes a not dissimilar confounding of expectations inside too.

The boy of the cover, Tighe, lives on the worldwall, as does everyone else. The wall has no apparent top or bottom, it simply goes on forever and everybody lives upon it. Theirs is a precarious existence largely concerned with mere survival, although travelling tinkers sometimes come bringing miraculous (but old) electronic and plastic devices to entertain the village-folk. One day, as is wont to happen, Tighe trips off the ledge of his village and falls a long way down the wall. Miraculously he survives and discovers the world is not anything like he has ever imagined. If anything the world is worse than he has ever imagined: a harsh, cruel and utterly amoral place where people die without reason and kill for even less.

What Roberts has tried to do, I suspect, is create a world turned upon its head that lacks any truly defining logic or morality, as he did in Salt; but whereas that book saw well defined and opposing ideologies fighting each other, On almost feels as though it is taking on the nature of the universe (in more ways than one).

Tighe's travels up, down and across the worldwall are not particularly edifying, he unearths no great knowledge or revelation from all his suffering, he is little improved as a boy or a man and has little effect upon the world (despite occasional and unfounded claims for his importance). He is a cog in the machine.

As I said to begin with, On is an unusual and thought-provoking book that avoids clichés and admits no easy readings. This can make for a frustrating reading experience at times but bodes well, I think, for Roberts' future development as a writer. He could become very important indeed.