The film begins with a man (mentioned in the credits as the “Thief”) who seems to be harvesting a type of larva for the peculiar effects it has on the human mind when ingested.
At a club, Kris (Amy Seimetz) is tasered and is kidnapped by the Thief. He makes her swallow the larva, which induces a sort of hypnotic susceptibility, which causes an extremely suggestible mental state that the Thief then exploits. He uses an elaborate set of distractions, such as getting her to create a paper chain where each link features a transcription from the book Walden, in order to distract her while performing his mind control. He eventually manipulates her to liquidate her home equity, reveal to him a stash of valuable rare coins and empties her bank account. Through hypnotic suggestion, Kris is prevented from consuming solid foods. She is only allowed to drink small portions of water at regulated intervals, which she is compelled to perceive as extremely refreshing and delicious. Thief eventually releases Kris, who binges ravenously and falls asleep in soiled clothes in her home. She awakens to find several large worms visibly crawling under her skin. She unsuccessfully attempts to remove them by using a kitchen knife.
Later, a pig farmer and avid field recorder—the “Sampler”—draws Kris to his farm using infrasonics. The Sampler silently sets up a transfusion through which he transfers a worm from Kris’s body into that of a young pig. Kris then awakens in an abandoned SUV on the freeway with no memory of these recent traumatic events. Upon arriving at her disordered house, she quizzically notices blood on her sheets and floors and considers calling the police. She realizes she has no information to tell them and stops dialing. After cleaning up, she heads to work, where she is promptly fired for her unexplained absence. A trip to the grocery store reveals to Kris that her personal funds are gone.
A year later, Kris meets a man named Jeff (Shane Carruth) on a train and connects with him. Kris and Jeff meet several times, before finally spending the night with each other. Afterwards, they realize that they both retain identical stitching scars from the aforementioned, forgotten, transfusions. The two of them soon realize that they both had similar experiences; Jeff lost his job as a broker due to shifting company funds around to cover for money stolen from him and attributed the incident to drug abuse. At the same time, it is made clear to the audience that a parallel exists between the emotions Kris and Jeff have been feeling and two pigs, one of which is the host to Kris’s parasite. As an example: Kris mistakenly believes herself to be pregnant at the same time her pig counterpart is actually pregnant. Upon consultation with a doctor, she is diagnosed with having had endometrial cancer that was successfully removed. The supposed cancer, she is told, is no longer a threat to her body, but it has rendered her infertile.
The Sampler finds that the pig containing Kris’s worm has now given birth to piglets. He throws the piglets into a burlap sack and tosses them into a river. This event coincides with Jeff and Kris feeling an extreme sense of loss and frustration, and both act as if something terrible is happening to them; Jeff spontaneously picks a fight with two of his co-workers while Kris frantically searches as if she’d lost something. The two, in their panicked state, reunite and travel to Kris’s house, where they gather supplies, including a gun, and make camp in her bathroom’s tub, expecting the worst. Meanwhile, the sack of piglets is seen rotting away and a blue substance bursts from the piglets’ open wounds, filling the surrounding waters, from which orchids have emerged. The orchids eventually turn the same color blue and are collected by farmers, who sell the plants in the neighborhood where the Thief operates.
These events seem to mark a change in the state of things. Kris and Jeff begin to remember each other’s personal histories as their own. Jeff discovers Kris mumbling the text of Walden while swimming. It is while performing this ritual that Kris comes to sense things that the Sampler has sensed, and it is this moment that the two start to piece together what happened to them both. In a dreamlike sequence, Kris, Jeff, and the Sampler all sit down at the same table in a bare, white room where Kris reveals to the Sampler that she is aware of him; the Sampler collapses from an apparent heart attack. The scene then cuts suddenly to a parallel shot back at the pig farm, where Kris shoots and kills the collapsed Sampler. Kris and Jeff collect a box of written records revealing others who were similarly drugged, and the two summon these other past victims to the farm by sending them copies of Walden. The farm is thereafter remodeled and the pigs are better cared for; as a result, no more pigs are drowned, the orchids in the river no longer turn blue, and the Thief is deprived of the larvae for his drug. The film ends with Kris cradling a baby pig, at peace.