Ten years ago, Jeff VanderMeer published the three volumes of the Southern Reach trilogy, which between them charted the incursion of the otherworldly into a stretch of Florida coastland. In Annihilation, scientists venture into what has been dubbed “Area X” and quickly find themselves physically and psychologically transformed. Authority follows a middle manager who, in the wake of this mission’s failure, is dispatched by the shady “Central” to evaluate the people who have made studying Area X their life’s work. Acceptance jumps between timelines: the days preceding Area X’s creation, the weeks preceding the departure of the mission in Annihilation, and the aftermath of Authority, in which Area X breaks its bounds and seems set to transform the world.

VanderMeer had until this point been a respected fantasy author, a stalwart of the New Weird alongside such authors as China Miéville, KJ Bishop and Steph Swainston. The Southern Reach trilogy, despite shifting its register into science-horror, utilised many of the same techniques as his previous novels: it took the queasy sense that there is an under layer to reality from City of Saints and Madmen (2001); the Nabokovian intercutting of text and commentary from Shriek: An Afterword (2006); the transformation of a familiar, rational space into an uncanny one, in which the boundary between human, animal and plant is no longer discernible, from Veniss Underground (2003).

Inspired by “Zone” SF such as the Strugatsky Brothers’ 1972 novel Roadside Picnic (adapted for screen as Stalker by Andrei Tarkovsky), the innovation of the Southern Reach books – and perhaps the reason for their global popularity – was in setting this eruption of weirdness in the familiar, present-day world, and tying it to contemporary concerns, such as a government that has become alienated from and hostile towards its citizens, or a natural environment on the verge of striking back at its despoilers (VanderMeer is also an environmental activist, calling for the preservation of the Florida wetlands that have inspired Area X’s landscape).

Absolution, the unlooked-for follow-up to the trilogy, seems at first glance like a series of outtakes from it, featuring familiar names and previously unknown backstory. Twenty years before the event that triggers Area X’s emergence, a scientific expedition – secretly bankrolled by Central – encounters harbingers of weirdness, such as the appearance of thousands of cannibalistic rabbits, and a mysterious figure dubbed the Rogue. And then 18 months before the event, a disgraced Central agent known as Old Jim is dispatched to the region to investigate the expedition’s failure and find the Rogue. A year after the event, that first expedition into the site – whose failure looms over the scientists in Annihilation – is related to us in the drug-addled, profanity-laden voice of one Lowry, whom readers of the earlier book will recognise as the expedition’s sole survivor.

Much of what made the original Southern Reach books powerful and disturbing can be found in this new volume. Once again, VanderMeer produces a near-seamless shading between the weirdness and danger of Area X, and the natural environment that preceded it. Old Jim is rattled by a stand of trees left dead by the inland incursion of seawater, seeing in it a hint of the unearthly, while a superintelligent alligator who is the Rogue’s companion disappears into the swampland. For the bureaucrats at Central, obsessed with “foreign interference” – a term whose vagueness obscures many possible meanings – this liminal quality is untenable. They send wave upon wave of operatives – as Absolution reveals, the ones we knew of were preceded by others – to unravel it. Invariably, once these operatives learn to understand Area X, they realise that they have become too altered by it to explain it to others, or even to return from it.

There is, however, a shift in Absolution’s focus, one that perhaps reflects the intervening decade of real-world events. The original Southern Reach books often featured grey bureaucrats attempting to quantify the indescribable. Absolution turns its attention to these bureaucrats, in the process revealing that they are not so grey. Central may in fact be a greater danger than Area X, if only because its leaders remain convinced that they can weaponise it. Having learned the extent of his superiors’ manipulation of their own agents, and their involvement in the lead-up to Area X’s creation, Old Jim begins to think of Central as a “shadow, eaten up from the inside”. Lowry, whose official mission is to find the “off switch” that will return Area X to normality, embodies Central’s contradictions, veering erratically between a xenophobic desire to destroy Area X, and an almost romantic longing to be made one with it.

Readers looking for a solution to Area X’s mysteries in Absolution will come away puzzled. The novel adds new information to our understanding of the site and its genesis, but also opens new questions, and leaves some dangling loose ends. What it does do is reinforce the original series’ contention – that the boundary between the uncanny and the familiar is more porous than we realise – with the observation that sometimes, at the very heart of rationality, we may find madness.