NOTE: This spoiler was submitted by Jeremy
The film opens with a woman driving down a road until she reaches a field with two small donkeys. She gets out of her car and shoots one of the donkeys until it is dead.
We meet David (Colin Farrell) as he checks into the Hotel with his brother, who has been turned into a dog. In the City, people are given 45 days to find a romantic partner or else they are to be turned into an animal of their choice. David meets with the Hotel Manager (Olivia Colman) and says he would like to be turned into a lobster since they live to be 100 years.
During breakfast, David observes three women - the Heartless Woman (Angeliki Papoulia), who is said to have no emotions; the Biscuit Woman (Ashley Jensen), who is always seen with a small pack of biscuits; and the Nosebleed Woman (Jessica Barden). David becomes acquainted with two men - Robert (John C. Reilly), who speaks with a lisp; and John (Ben Whishaw), who walks with a limp. Later, during an assembly, John is called up to speak. He says that his father left his mother for another woman, and so she was turned into a wolf and brought to live in a zoo. He would visit her enclosure until he climbed in to give her a hug. The other wolves attacked him, leaving him with his limp, but two wolves stayed still, and he figured one of them was his mother.
Throughout their stay, the singles attend dances to meet one another. They are also given extra time by going on hunts and finding loners in the woods to tranquilize. The Heartless Woman is said to be the best hunter due to her cold and unfeeling nature. On the bus ride to the hunt, David sits next to the Biscuit Woman, who propositions him and then says she may jump out the window of her room.
Masturbation is restricted at the hotel, and so the men can only receive moderate sexual stimulation (without orgasm) from the Maid (Ariane Labed). The Hotel Manager finds out that Robert was masturbating repeatedly, and she forces him to have his fingers burnt in a toaster as punishment. Meanwhile, John pursues the Nosebleed Woman by faking a nosebleed problem by banging his face against something. They eventually fall in love and are moved to a bigger room for the two of them.
The Biscuit Woman jumps out her window and is left on the ground, bleeding and screaming in agony. David approaches the Heartless Woman and makes brash comments regarding the Biscuit Woman's demise. They then go into a jacuzzi together. The Heartless Woman pretends to choke on an olive from her martini, and when David doesn't try to help her, she decides they are a good match. The two are then moved into the bigger bedroom, though David must continue pretending to be as heartless as she is. They run into John and the Nosebleed Woman, along with a little girl named Elizabeth (Laoise Murphy) assigned to be their daughter. John tells Elizabeth to give David a kiss, but he responds by kicking her in the shin so she can limp like her dad.
The Heartless Woman tells David she killed his brother by kicking him repeatedly. She has blood on her leg. David pretends to be unmoved, but when he sees the dead dog in the bathroom, he starts crying, and the Heartless Woman slaps him for lying. She goes to tell the Hotel Manager, but, with help from the Maid, David tranquilizes the Heartless Woman and drags her into the transformation room to be turned into an unknown animal.
David flees from the Hotel and goes into the woods where he meets a group of Loners. The Loner Leader (Lea Seydoux) welcomes David, but tells him that any romantic interaction is forbidden and is punishable. David sees one man with bandages on his mouth. He is told that the man was given "the red kiss", in which he had his lips cut off, along with another woman who suffered the same fate, and they were forced to kiss each other. The worse punishment is said to be "the red intercourse", which one can only imagine as to how it goes.
During his stay there, David falls for the Short-Sighted Woman (Rachel Weisz). He wins her over by catching and killing rabbits, and then cooking them in a way specific to her liking. David also encounters Robert, who wants to shoot him and bring him back to the Hotel, but the Short-Sighted Woman knocks him out.
The Loners take trips into the city pretending to be couples. David is paired with the Short-Sighted Woman, and they are able to go by as a real couple without trouble. It is also revealed that the Maid is working with the Loner Leader and gathering information from the Hotel.
The Loners then break into the Hotel while David boards a yacht that John and his new family are in. David tries to break them up, but neither of them want to hear what he has to say, and he leaves the yacht. In the Hotel, the Loner Leader goes into the room of the Hotel Manager and her husband. She holds the Manager at gunpoint and asks her husband if he loves her. He says yes, but when given a gun to shoot her, the husband pulls the trigger, but the gun is empty. The Loners leave the two alone.
The Loner Leader notices how close David and the Short-Sighted Woman have become. She then discovers the woman's journal and reads about her plan to escape with David into the City. The Loner Leader and the Maid take the Short-Sighted Woman into the City to have an operation that they claim will cure her vision, but in reality, they have her blinded. The woman is left to defend herself with a knife, which the other two women try to take away from her, but the woman stabs the Maid and leaves her to die.
Later, David attacks the Loner Leader and ties her up. He throws her in an open grave and leaves her to the mercy of some wild dogs.
David and the Short-Sighted Woman flee into the City. They go into a restaurant and sit together for a while. David goes into the bathroom and takes a knife with which he attempts to blind himself. We never find out if he goes through with it.