Jeff VanderMeer‘s novel Annihilation is an experience. The first entry in his best-selling Southern Reach Trilogy, it follows a team of female scientists who enter a mysterious biological anomaly, hoping to study its interior and uncover its origins. Most who enter never leave, and those on the outside want to know why.

Though Alex Garland‘s latest sci-fi film shares a title and basic premise with VanderMeer’s novel, the movie diverges greatly from its source material. Garland first read VanderMeer’s book as a galley when he was wrapping up post-production on Ex Machina. In an interview with Nerdist, he confessed that he wrote the screenplay before VanderMeer released the next two books in the trilogy, and that he completely changed almost everything about it, especially the ending. In a recent Q&A, he even admitted that he only read the book once, and adapted it from memory.

The result is something that honors the book’s surrealism while forging its own unique path. Here are all the major changes Garland made.

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Area X / The Shimmer

In the book, the mysterious anomaly is called Area X. In the film, Area X is mentioned in a title card, but refers to the plot of land just beyond the anomaly, where the government has set up an observational base. The book’s Area X is called the Shimmer in the film in reference to its oily, iridescent physicality.

Area X is no secret in VanderMeer’s novel. The public is well aware of its sudden appearance. This isn’t the case in the film; when Kane (Oscar Isaac) is about to depart for his expedition, he can’t tell his biologist wife Lena (Natalie Portman) where he’s headed. It’s not until his return and subsequent hospitalization that Lena is clued into what’s going on, before she also decides to infiltrate the Shimmer.

The Tower

One of the book’s creepier elements is a manmade structure the group encounters in Area X that they call “the Tunnel,” but that the biologist calls “the Tower” for reasons she has trouble articulating. (In the third book, Acceptance, it’s revealed that she used to live in the area before its transformation.) The structure is a hole in the ground containing a staircase that descends deep into the earth. The walls of the tower appear to “breathe,” and on them is etched an eerie passage of writing that reads like gibberish (or the title of a Fiona Apple record):

“Where lies the strangling fruit that came from the hand of the sinner I shall bring forth the seeds of the dead to share with the worms that gather in the darkness and surround the world with the power of their lives while from the dim lit halls of other places forms that never were and never could be writhe for the impatience of the few who never saw what could have been.”

The words appear to be written not in ink but in some kind of plant, which later infects the biologist when she touches it. We also learn that the author of the script is a being called the Crawler, who later kills one of the team members.

The film forgoes the tower plot almost entirely, although the lighthouse in the final act contains a hole in the ground that is reminiscent of this element in the book.

The team and their fates

The book refers to the all-female team of explorers only by their titles: psychologist, biologist, anthropologist, surveyor, linguist. The linguist abandons the group before they enter Area X, and so the focus is only on four of the women. The anthropologist is killed off pretty quickly (presumably by the Crawler), the surveyor is killed by the biologist once she goes crazy, and the psychologist disappears.

Garland restructured the team and fleshed out each member. The psychologist (Jennifer Jason Leigh) and the biologist, Lena, are fairly similar to their novel counterparts, but the other three members have different roles and functions. Gina Rodriguez plays a paramedic named Anya Thorensen, Tuva Novotny plays a magnetologist named Cass Sheppard, and Tessa Thompson plays a physicist named Josie Radek.

Unlike the book, the film gives each of these women a reason for entering the Shimmer: Thorensen is an addict, Sheppard lost a child to cancer, and Radek is a self-harming depressive. “We’re damaged goods,” Sheppard tells Lena in one pivotal scene. Shouldering the weight of a suffering marriage, Lena is also given a new reason for joining the team. Likewise, the psychologist, Dr. Ventress, comes along because she’s dying of terminal cancer and hopes to find purpose in the Shimmer; this is actually also true of her book counterpart, although that motivation isn’t revealed until later in the series.

All of their fates are ultimately different than in the book. Sheppard and Thorensen are both killed by a bear-like creature with an exposed skull, Radek willingly relinquishes herself to the Shimmer’s biological power, and the psychologist makes it to the lighthouse, where she transcends her physical form and is “annihilated” by an extraterrestrial force.

The Southern Reach

VanderMeer’s trilogy is named after a governmental agency tasked with investigating Area X. In the first book, their involvement in the expedition creates a fair amount of infighting and paranoia. For instance, as instructed by the Southern Reach, the psychologist has programmed the rest of the team via hypnosis. The book’s title is actually a reference to one of the hypnotic triggers: if things go awry, the word “annihilation” will cause any team member who hears it to commit suicide. (In the film, the title is a reference to the extraterrestrial’s ostensible desire to “annihilate” mankind.)

Southern Reach gets a quick shoutout in the film, but doesn’t play much of a role beyond that. The hypnotic triggers aren’t mentioned and their involvement in the expedition isn’t important.

Lena’s husband

The biologist’s husband is dead before the novel Annihilation even starts—rather, his “copy” is dead. Similar to the film, the book reveals that the man who returned from his expedition wasn’t who he appeared to be, but rather a duplicate forged in the anomaly. The duplicate dies of cancer, prompting the biologist to go on her own mission to Area X. While there, she discovers her husband’s diaries in the tower, and realizes he may still be alive. The book ends with the biologist deciding to remain in Area X until she finds him.

In the movie, Kane kills himself with a phosphorous grenade in the Shimmer’s lighthouse and his copy escapes. But the copy doesn’t die, and is reunited with Lena (or “Lena”) in the end.

The ending

Where to begin? The book’s finale is pretty clear cut: everyone else is dead, the biologist decides to stay in Area X. But the film decides to go in an entirely new direction, getting downright psychedelic in the process. Lena reaches the Shimmer’s mysterious lighthouse and discovers a camcorder that recorded her husband’s suicide. Realizing the man she saw on the other side wasn’t her husband after all temporarily throws her, but then she notices a hole in the wall and climbs into it, where she finds the psychologist, who is communicating with some sort of glob of molecules and matter.

The psychologist becomes one with this prism of energy, which exposes itself to Lena. She climbs back out of the hole and is barred from escape by the glob, which has taken humanoid form. The presence attempts to mirror Lena’s actions, and she quickly realizes it’s trying to duplicate her the way it did her husband. She’s able to trick it, and “kills” it with the same type of grenade her husband used to kill himself. She leaves the Shimmer and returns to the Southern Reach facility, where she explains her trip to a room full of doctors. She reunites with her “husband,” who admits he’s not really Kane. He asks Lena if she’s really herself, and she doesn’t answer—instead, they embrace and her eyes glow the same as his. We’re left to ponder if this is the real Lena, an irrevocably changed Lena, or a duplicate Lena.

Though VanderMeer’s novels continued after Annihilation, Garland has made it clear that his movie is meant to be a standalone. After that breathless finale, and the general wrapping up of all things Shimmer-related, it would appear he’s telling the truth. It may be the end, but that doesn’t mean you’ll stop thinking about it any time soon.

Image: Paramount Pictures

More on Annihilation!

• Read our review of the film!
• 13 movies to watch after Annihilation
• The scariest part of Annihilation is the unknown