There isn't actually a lot that happens in the movie. Scarlett Johansson's unnamed alien drives around Glasgow, picking up lonely men and luring them back to her abode. There, to the sounds of spare, pulsating synths, she slowly strips, leading them deeper and deeper into her room, black and empty, the floor reflecting their forms like a mirror. As the men disrobe, they begin to sink into the surface of the floor. The imagery is like a nightmare; they sink like stones and then float beneath the surface, weightless, until some unknown force drains them, leaving only empty skin drifting in the water like a ghost, or a wisp of smoke.
A change seems to occur when she is trying to seduce a new victim on the a rocky beach. He spots a couple drowning and dashing off, trying (and failing) to save them. When he makes it back to the beach, exhausted and half-drowned himself, she hits him over the head with a rock and drags him off. He is not seen again, and outwardly she is unmoved. However, she can't finish the job with her next victim, a young man with facial deformities. After she gives him to the room, there is a scene where she spends several long moments staring into a mirror, and the raw emotion on her face marks her internal change. Up until now, she's been utterly unreadable, expressionless except when she's chatting up her victims. She lets him go, and then takes off herself.
She isn't the only alien on the planet. There is another one, a man, who seems to watch her and clean up after her if there is any trace left of her victims. It turns out he is one of four, and when she runs, they pursue her. They, too, are like something out of a nightmare. There's something relentless about the way their motorcycles eat up the road, and the way the will sometimes stop and seem to scent the air reminded me a bit of a hunting hound.
She looks for safety in increasingly remote areas, leaving the city for a rural town, where a man takes her in and gives her shelter, and then for a forest, where a logger attacks her. The further she gets from the city, the more human she seems. For the first time you see fear in her, vulnerability, sadness. It seems like she tries to make a connection with the man who tries to help her, even offering him her body, which she had formerly only used to lure in her victims. It seems, however, that she is not equipped to consummate the act.
The scenes that were the most dynamic, and the most thematically interesting to me, where the ones in the forest. All throughout the movie, she has been the predator, the one using smiles and questions to bring in her prey. When she encounters the logger in the forest, he mirrors her earlier behavior, acting friendly and helpful, just slightly too familiar for the circumstances. The moments between when she meets him and when he attacks are are some of the tensest in the film. She is now prey, but it doesn't seem as if she senses the same thing that we do.
There are certain motifs that run through the film - the masks that people wear, the relationship between predator and prey, coming to grips with our emotions and needs and how that conflicts with our duties - but it's hard to ascribe meaning to it as a whole. I don't know if it's meant to have a meaning or a moral, although some things make me think that it does. Her emotional awakening, if you want to call it that, comes from an encounter with a man who looks monstrous, but is deeply sensitive and lonely. After she has a terrible and violent encounter with another man, who is monstrous on the inside, her inner monster is revealed. I don't really know what it's supposed to mean, but it clearly means something.
It is a deeply unsettling film. After I left the theater, I couldn't really even form complete thoughts for a while. I felt like I was an alien myself, or as if I'd been jarred out of reality and had to find my way back. In that way, I guess I would say that it's a very successful film, although I honestly couldn't tell you if I actually liked it or not.