As you might expect, this piece features major plot spoilers for Annihilation. If you haven't seen it and want to remain unspoiled, please read our non-spoilery review. Otherwise, we're gonna take trip into the spoiler-shimmer.
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Alex Garland's Annihilation is a mind-bending sci-fi epic with a lot to say – and a lot to piece together. In the vein of 2001: A Space Odyssey, Under the Skin, and other genre staples that provoke without answering, Annihilation rips open the id, questioning the finality of human biology and our tendencies toward self-destruction. It also introduces a truly singular and fascinating setting in "the Shimmer," a scientific anomaly where much of the film takes place. The Shimmer is an update on the book's themes, giving the movie its own motivation. But what exactly is the Shimmer? And how does it tie into the mystifying – and downright mystical – ending? Let's dig in.
What is the Shimmer?
In Jeff VanderMeer's novel, Annihilation, the mysterious anomaly that appears out of nowhere is referred to as Area X. It doesn't have the same oily, iridescent quality that its film counterpart does. It's merely a dreamy, odd plot of perverted biology containing unknowable creatures and a structure called the "the tower" – which houses an odd, descending staircase where much of the book's craziness takes place.
The film reimagines a lot of what the novel posited, renaming the area the "Shimmer" and further explaining its bizarre qualities. As Tessa Thompson's physicist character Josie Radek observes, the Shimmer is actually a prism, but it doesn't just reflect light; it also reflects DNA and other physical properties. When the all-female team infiltrates the Shimmer, they are subjected to its utter lack of reason: Time is warped, their equipment malfunctions, compasses spin. This is no easily traceable phenomena. The Shimmer is something different, something extraterrestrial.
The story of Annihilation is told non-linearly. We open with a biologist named Lena (Natalie Portman) recounting her infiltration of the Shimmer, as well as her escape. She was part of the 12th expedition into the anomaly, only entering after her husband Kane (Oscar Isaac) returned from his own government-ordered Shimmer penetration. Kane's trip proved cataclysmic; he was the only survivor, and returned to the real world with massive radiation poisoning. Lena enters the Shimmer of her own accord, hoping to gather the information her husband could not, and also hoping to rediscover herself along the way.
Along with a psychologist, a magnetologist, a paramedic, and a physicist, Lena willingly penetrates the Shimmer. At first, things are weird (they lose a few days), but not too crazy. But as they get closer to the lighthouse – the most affected structure in the Shimmer – the scientists observe increasingly bizarre happenings. A crocodile with an extra row of teeth attacks them in a boathouse, and a crazed bear creature mauls and kills two team members, acquiring one of their screams in a scene so freakish and terrifying that it's already infamous. The scientists start to uncover the prism's properties, including its ability to mutate and duplicate matter. Once the suicidal Radek is fully aware of where she is, she allows herself to be overtaken by the Shimmer's biological power. By the end, only Lena and Dr. Ventress (Jennifer Jason Leigh) remain.
What is the ending trying to say?
Lena eventually finds her way to the lighthouse, where she discovers Kane's seared corpse, and realizes the husband she thought escaped was actually a physical duplicate. She enters a hole in the lighthouse's wall where she finds Ventress, who is fully giving herself over to the powerful extraterrestrial force that created the Shimmer. Ventress, who is now enlightened to the alien's modus operandi, informs Lena that the being lacks a consciousness but does have a driving force: it wants to annihilate human biology and rebuild it from a molecular level.
Ventress "dies" but the being accumulates her matter and refocuses it into a strange chunk of iridescent anatomy, which presents itself to Lena. It then takes a humanoid form and attempts to duplicate Lena's physicality. Lena tries to escape, but the humanoid traps her, locking her into a tête-à-tête of reconfiguration. Lena is able to outsmart this other being, and hands it a phosphorous grenade that winds up killing both the humanoid and the entire Shimmer in the process. The disintegration of the Shimmer allows for Lena's escape back into the real world, where she is reunited with her "husband."
Lena might not be who she says she is
In the end, Lena is reunited with Kane in the Southern Reach facility. She asks him a simple question: "Are you my husband?" He isn't quite sure. And of course, he's not really Kane – we saw the real Kane commit suicide with a grenade in the lighthouse. But is she Lena? Kane asks her this and she doesn't answer, but instead embraces him before we see her eyes glow, similar to his.
While this might seem to indicate that Lena isn't really Lena, the actual answer might be more complicated. As we learned earlier in the film, Lena was "infected" by the prism. At one point, she studies her blood and realizes it's been manipulated. That means that no matter what, she's exiting the Shimmer with complications. That would allow for her eye glimmer and for her odd behavior after leaving the anomaly. The film is intentionally ambiguous about the real answer here – but in a way that makes it everlasting, the sort of sci-fi possibility we'll be questioning forevermore.