IN REJOICE, A Knife to the Heart by Steven Erikson (Gollancz, £18.99), the aliens have arrived and they're on a mission familiar to SF fans — to rescue the Earth from its human despoilers and, in doing so, pass judgment on the fate of humanity.

As the interface between us and their almost omnipotent artificial intelligence, they choose a chain-smoking, wise-cracking science-fiction writer who regularly receives death threats for her outspoken and wildly undiplomatic blogging.

By way of a start, the AI makes violent acts by humans against each other or against their biome impossible, thus disabling — if not yet ending — the nation state, since that can only exist with enforceable boundaries.

The system of hierarchical government also becomes a practical dead duck as, in the final resort, it must be backed up by the threat of violence. Then, by ensuring everyone has food and fresh water, the visitors start introducing us to an age of post-scarcity, which of course means that capitalism no longer has a market in which it can function.

There's little attempt by the author to turn all this into a narrative novel, rather than a procession of thought experiments and jokes. But that doesn't really matter, because the gags are good and the concepts fascinating.

There's another examination of post-scarcity in By The Pricking of her Thumb by Adam Roberts (Gollancz, £16.99). It's the second of his whodunits set in a near-future Britain where most people spend most of their lives in the Shine, a kind of virtual reality super-internet.

Private eye Alma has good reasons for avoiding immersion there , so she specialises in investigating crimes that take place in the almost deserted real world.

Her client in this case believes that one of the four richest tycoons in Europe, who are competing with each other to achieve a state they call "absolute wealth," is dead.

Alma's far from simple task is to find out which one and to do so she will need to solve a more fundamental puzzle — when almost all wants are now met in the Shine, what is money for? When financial rationing loses its power, what will money become?

Written in a witty, playful and almost teasing style, this is an impressive novel of ideas and a moving love story as well as a tense mystery thriller.

Teenager Spensa lives underground in Skyward by Brandon Sanderson (Gollancz, £18.99), on a planet that may well be the last refuge of a human diaspora under constant attack from a mysterious alien race.

Humanity's only defence comes from the heroic pilots who fight a kind of futuristic Battle of Britain in the skies above. Spensa dreams of joining them, like her father before her, but the circumstances of his death have left her family name tainted.

This deeply entertaining first episode in a series is for fans of aerial warfare stories in which the characters are as well-devised as the machines.