Jeff VanderMeer has been called “the poet laureate of weird fiction,” the “king of weird fiction” and “weird Thoreau.”

So it’s notable that VanderMeer says his new novel, “Absolution,” is his weirdest book yet.

“Absolution” is an eerie and unsettling coda to the books that make up his best-selling Southern Reach trilogy, which were published in quick succession in 2014. The series went on to sell more than 1.5 million copies in the United States alone, and was translated into 37 languages. In the first three novels — “Annihilation,” “Authority” and “Acceptance” — a shadowy agency sends ill-fated expeditions of researchers into a contaminated region on the Forgotten Coast called Area X, where human inhabitants have mysteriously disappeared and the plants and animals have undergone strange mutations, evolving into something alien. When the series concluded, Area X was spreading, and readers were left pondering the fate of humanity and the planet.

VanderMeer delighted fans this year when he announced he’d written a surprise fourth volume. And in his trademark hallucinatory fashion, the new novel delivers as many questions as answers.

The fourth book, “Absolution,” goes back 20 years to the Forgotten Coast, the region where the mysterious aberrations first began to manifest. In three sections, Vandermeer chronicles three missions to explore and understand the region, which all go horribly wrong in different ways. The first section follows a group of biologists who witness strange and unnerving animal behavior. The second centers on an operative for Central, a secret agency, who comes to realize that he is being manipulated by his handler. The final section is a trippy, expletive-laced first person account from a soldier named Lowry who is sent on a reconnaissance mission into Area X — and steadily loses his mind as he confronts the incomprehensible.

During a video interview from his home in Tallahassee, Fla., Vandermeer spoke about why he wanted to return to Area X, how he’s kept the mystery alive for a decade and why he thinks alligators are misunderstood.