The 21st century hasn't gone well. The Last War has engulfed the world in cataclysmic battles and plagues; only the forward thinking of Plato, a millionaire businessman on the islands of Aotearoa (New Zealand, to you and me), saved his country. He built the Great Sea Fence around the entire Republic (that would be, ahem, Plato's Republic) to keep out a planet full of desperate refugees. Isolated, the republic thrived, and as communications stopped being received from the rest of the world, it became, quite literally, the last outlet of civilisation on the face of the Earth.

All was not well, though. The citizens were kept in line mainly out of fear, and as the threat of infection and war seemed to dissipate over the decades, so did the republic's control over the populace. Until one day border guard Adam Forde made a fateful decision when a refugee appeared at a section of the fence he was overseeing, setting off a chain of events culminating in the Great War, the event that irreparably changed not only the republic, but the entire world.

Bernard Beckett's Genesis is set some time later, when young student Anaximander is being interviewed by three examiners for a place in the exclusive academy, which accepts less than 1% of all applicants. With her beloved tutor Pericles, Anax has studied the life of Adam Forde for three solid years. She has a risky theory to propound about Forde's true place in their history, a theory that might clash with the academy's official order of events.

Her interview, all five hours of it, makes up the entirety of Genesis, a daring formal experiment that may not always work dramatically, but has a palate-cleansing purity unusual in most young adult fiction. Unsurprisingly, given the plethora of Greek names - Plato, Pericles, even Anaximander was a real philosopher - the novel takes the form of a Socratic dialogue, with pages of Anax and her examiners exchanging views.

Anax describes the events of Forde's life in great, sometimes improbable, detail, creating holograms to illustrate her points. There are, in fact, times when Genesis feels a bit like sitting in on a doctoral defence, but this also allows Beckett to expound his ideas with admirable economy. "Human spirit," he says, "is the ability to face the uncertainty of the future with curiosity and optimism." It's this spirit which we discard at our great peril. Fear is the killer of our species, he argues, allowing us to be easily manipulated by our leaders and by each other.

When Forde rescued the girl, the government used his show trial as an opportunity to scare the populace once again with threats of incomers and fear of the unknown. This had unexpected consequences, and as a creative punishment he was incarcerated with Art, an artificial intelligence android with the face of an orang-utan, ostensibly to let Art learn from the interaction but in the vague hope that Art might kill Forde in an "accident".

Art soon grew far more intelligent than expected, though, drifting into possible real consciousness. As Anax digs deeper and deeper into her interview, she reaches towards information she feels is missing about Art's true place in the republic's history and a secret slowly begins to surface, one that provides a Twilight Zone-style moral twist to the proceedings. Beckett has written a very different young adult novel - assured, cool, almost cold - that will make smart teenagers feel very respected.

 Patrick Ness's The Ask and the Answer is published by Walker Books.