Lethe is set in 2166, eighty years after genetic warfare has changed the world forever. The cleanup operation is still in progress; purple algae process the toxins from the seabed, and a variety of new species have arisen to fill drastically-changed ecological niches. Meanwhile, the majority of Earth's remaining human population live in reservations, shielded from the poisonous elements and the merciless sun. Outside the rezzes, One-Eyes - mutated human stock - perform the menial tasks that keep the pure humans alive. And in the high tower of the League of New Alchemists - so-called because they transmute matter, in this case their own flesh - live the Brains, who administer this grim new world. The Brains (or Pickled Heads, as they're known 'behind their backs') are bodiless arrays of tissue, connected to the world through a permanent interface - the appalling results of biological experimentation from the days before the Gene Wars. The work of the League - ranging from terraforming the Moon to developing 'only slightly radioactive' crops - is carried out largely by altermoders, products of genetic manipulation who can switch from their human state to an aquatic form in which they communicate with dolphin pods. The dolphin-altermode symbiosis provides massive 'computing' power, which can be applied to almost any problem.
The latest 'problem' is a real teaser. Jenae and her dolphins are asked to interpret a mysterious transmission picked up from Underkohling, an artifact of unknown origin on the outskirts of the solar system. Underkohling's mysteries have already been probed, to no effect. It holds four 'gates'; two lead to uncharted areas of space, one to somewhere that no probe has ever returned from - and the fourth gate appears at unpredictable intervals. Its latest appearance coincided with the presence of software expert Daire Morales, who was searching for the source of the transmission. It's swallowed him whole. Whether he found the source is a matter for debate.
The transmission which Jenae attempts to decode refers to the ship 'Morpheus', which crashed on Underkohling at the height of the Gene Wars, carrying the Board of Ingenix - one of the three companies who, between them, tried to remake the world. Could 'Morpheus' have passed through the fourth gate? Could the gate lead to a new, unsullied world?
Daire, of course, knows the answers; getting them back to Earth, however, poses problems. And the answers pose more questions that he cannot answer. What are the ghosts? Is he a ghost himself? Where is he?
Jenae's discoveries put her in an equally untenable position - one that is even more dangerous. Her obsessive quest for justice leads her from the desert wastes of New Zealand to the uncomfortable cosiness of 22nd-century Oxford - and through the oceans between.
Lethe shows us a future that's distinctly dystopic. Nature is now inimical to human life, and human life knows it only too well. 'Humanity, that once sought to control the world, has succeeded only in changing it, and now ... evolution has taken off like a house on fire ... The world's not (our) playhouse any longer. It's a great big ravenous entropic thing.' That's the ivory tower perspective of an Oxford don. Keila, the One-Eye, might say the same thing; but, on the other hand, she has mutated and survived. This is a world where, more than ever, your DNA dictates your chances of survival. The fight to regain a small part of the earth for humans is a grim one, and the human tragedies which result cannot be allowed to interfere with that reclamation. Jenae's twin sister Yi Ling carries the gene for altermode, but is not an altermode herself; Daire also carries the latent gene. Both will come to regret their genotype, for very different reasons.
Lethe deals uncompromisingly - and unpedantically - with one of the recurring themes of science fiction - what it means to be human. Is it in the genes? The brain? The 'soul'? Lethe doesn't offer us any real answers; but the questions are posed in new and intriguing ways, inviting us to consider all the implications of genetic manipulation. Sullivan's rigorously constructed future contains little that is fanciful - and much that is poetic. As Daire says at one point, 'anything is possible ... you just have to suspend your belief in reality.' The reality offered in this novel is disturbingly plausible, as convoluted as a naked brain, and brilliantly described. An astonishing debut.