NOTE: This spoiler was submitted by Jeremy

The film starts in a hospital delivery room where Mona Wassermann (Zoe Lister-Jones) is giving birth to her son, Beau. Through muffled dialogue and barely visible footage, it sounds as though Beau was dropped, and Mona is panicking. The doctor slaps Beau’s butt, and he lets out a cry.

In the present, Beau (Joaquin Phoenix) is visiting his therapist, Dr. Jeremy Strand (Stephen McKinley Henderson), discussing his relationship with Mona (now played by Patti LuPone). Beau is set to visit Mona but has some reservations about it. He discusses his feelings about growing up with her, including mentioning a recurring dream he has where Mona is trying to force Beau (as a child) to take a bath. Dr. Strand gives Beau a prescription for an experimental drug.

Beau lives in a rundown apartment in a neighborhood full of deviants and drug-addicted homeless people, including one deranged naked man (Bradley Fisher) who stabs random pedestrians. Beau tries to sleep before his flight the next day, but one of his neighbors plays loud music, and another neighbor mistakenly believes Beau is the one playing the music, so they leave warning notes under his door every hour.

Beau wakes up the next day around 3:30 in the afternoon, roughly two hours before his scheduled flight. Just as he is about to head out the door, he realizes he forgot something, and when he goes back to the front, he finds that his key and luggage were stolen by the irate neighbor. Beau calls Mona to explain his situation, but she seems to think he is just making up an excuse not to go visit her.

Later, Beau tries to take the medication, but the water in the building has been shut off, and he has already swallowed the pill without taking water when he needs it with the pill. Beau leaves a phone book to prop open the building door so he can run across the street to a convenience store for water, evading a crazy tattooed homeless man (Karl Roy) and another needy man asking for help. Beau tries to pay for the water but has his card declined, so he frantically tries to pay for the water while he watches everyone on the street gather into the building. Before Beau can make it back, he gets locked outside the building. He sits outside on the fire escape as he watches the people having a raucous party inside.

The next day, Beau re-enters the building since the front door was broken. He finds the tattooed man dead after being bitten in the neck by a brown recluse spider that’s loose in the building. Beau goes back to his apartment and finds that it has been vandalized. He then tries to call Mona, only to find a UPS worker (Bill Hader) answering the phone. The man claims that he found the phone and that Mona’s body was found decapitated when the chandelier in her house fell on her head. Beau is in shock and disbelief.

Beau attempts to take a bath and then finds something dripping on his head. He looks up and finds an intruder holding himself up on the ceiling, with his sweat falling onto Beau. He looks at Beau desperately but gets spooked when the spider crawls on his face. The intruder falls into the tub with Beau, leading to them awkwardly rolling around, trying to get off each other. Beau then runs out of the apartment nude and into the street, where a police officer tries to confront him at gunpoint. Beau runs away and then gets hit by a truck.

Beau wakes up from a coma two days later in the home of a couple, Roger (Nathan Lane) and Grace (Amy Ryan). They were driving the truck that hit Beau, and they brought him to their home to tend to his wounds. They live with their bratty teenage daughter Toni (Kylie Rogers), plus a mentally unstable veteran named Jeeves (Denis Menochet), who served with their son who was killed in action. Beau contacts his family’s lawyer Dr. Cohen (Richard Kind), who berates Beau for contacting days after Mona was found dead. He informs Beau that Mona’s body cannot be buried yet because it was her wish that Beau be present. Beau asks Roger and Grace to help him get home, but they insist that he stay with them until he has fully healed.

Beau continues to stay with the family, and Roger keeps coming up with reasons to delay Beau going home. Grace makes subtle hints to Beau about being watched, such as writing “stop incriminating yourself” on a napkin and showing him a channel where he is being recorded through a hidden camera. Beau later goes into Toni’s room and looks on her laptop to find news about his mother. A news report appears to confirm her death, reporting on her legacy as a highly successful CEO and businesswoman. Beau then sees that a woman he once knew, Elaine Bray (Parker Posey), worked for Mona, and it causes him to vomit on the laptop, which Toni sees.

Toni seems as though she is going to take Beau, along with her friend Liz (Alicia Rosario), but they just drive around the block before forcing Beau to smoke a joint laced with three different drugs. He declines until they threaten him by saying they will make it look like Beau harmed the girls. Beau smokes the joint and hallucinates seeing Elaine next to him. This leads to a flashback from when Beau was a teenager (played by Armen Nahapetian) meeting Elaine (played by Julia Antonelli) for the first time. They shared their first kiss together while staying at a resort. In the middle of the night, Elaine’s mother was forcing her to leave with her, so she ran to Beau’s room and kissed him in front of Mona, with the two of them promising to save themselves for sex with each other in the future. The flashback is interrupted by Beau waking up in the house from Toni screaming and throwing a tantrum.

When Beau is set to be taken home, he is brought by Toni into her brother’s old room and gives him a bucket of paint to go over the walls. Beau is confused until Toni seems to have a breakdown and say that he’s replacing her brother and wants him to drink paint with her. Toni chugs blue paint and dies. Grace walks in and sees Beau holding Toni’s body, leading her to angrily believe that Beau is responsible. Beau panics and runs through the glass door away from the house and into the woods. Grace orders Jeeves to find Beau and rip him apart.

Beau wanders through the dark woods for some time until he spots a young pregnant woman, Penelope (Hayley Squires), walking and singing. Beau asks her for help, and she guides him to her group of traveling theater performers called “The Orphans of the Forest.” He sits to watch a play of theirs, which details a young man going through a life after the death of his parents. An angelic figure details the protagonist’s journey – in which Beau sees himself in the position, going through a storybook-like path from youth to old age – going through many changes in his life. Old Beau meets his sons (Michael Gandolfini, Theodore Pellerin, and Mike Taylor). This confuses Beau because a flashback shows Mona telling him that the men in his family have a genetic heart murmur condition that killed them all when they had sex, so Beau had avoided physical contact. Outside the play, a strange man (Julian Richings) tells Beau he knows him and that he knows his father. Moments later, Jeeves shows up and begins to attack in his rampage for Beau, killing the lead actor with a knife and blowing some people up with a grenade. He appears to be brought down briefly when he gets kicked and shoots himself, but Beau manages to run away.

Beau is picked up by a driver and taken into Wasserton, the hometown named after Mona. He goes to her house and finds her headless body prepped for burial. After taking a nap, Beau awakens to find Elaine arriving at the house to leave flowers and comment that Mona owed her money. Beau catches up to her and tells her who he is, as Elaine did not immediately recognize him. She is happy to see him, and he tells her that he waited for her. The two go upstairs to get intimate. Beau finishes first, but Elaine continues until she appears to die mid-climax, frozen on top of Beau. As he panics, Beau then hears the voice of a woman talking to him – and it’s Mona, very much alive.

Mona has some of her employees take Elaine’s body out of the room as she talks to her son. She reveals that not only did she fake her death, but she has been keeping tabs on Beau the whole time. Dr. Strand worked for her (as did Roger and Grace), and he was recording his sessions with Beau. Beau says that he knew Mona faked her death because the body he saw had a birthmark that he recognized as belonging to their old housekeeper. Mona accuses Beau of not loving her and making excuses for not seeing her. She forces him into the attic that he dreaded going into as a child. There, Beau meets his real father – a giant penis-shaped monster. Jeeves then breaks in through the attic window, shooting and stabbing at the penis monster in the balls, only for the monster to stab Jeeves through the head with one of its legs. Beau runs back down the stairs and apologizes to Mona, only for her to berate him further and tell him that she always hated him. Beau starts to strangle Mona until he lets go, but she collapses, seemingly dead for real.

Beau runs outside and takes a boat out to sea, almost looking like he will escape until he ends up in an arena full of onlookers. Mona shows up with Dr. Cohen and puts Beau on trial, making him look like a bad son. Beau has a defense attorney present, only for one of Mona’s employees to push that man to his death. Beau is declared guilty and finds that his feet were glued to the inside of the boat. Although he pleads for Mona to help him, she doesn’t listen, and he accepts his fate when he sees the motor on the boat has caught fire. The motor explodes and capsizes the boat, causing Beau to drown. While there appears to be a struggle, the boat then goes still while Mona and Dr. Cohen leave.

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Beau Wassermann is a neurotic middle-aged man who lives by himself in a rundown apartment in a crime-filled city. He has a complicated relationship with his controlling mother, Mona, a successful CEO and businesswoman. Beau misses a flight to see Mona, and he later learns that Mona has apparently been killed in a freak accident.

In his attempts to return home for the burial, Beau encounters a number of strange events, including being kept in the home of a couple, Roger and Grace, with their bratty teenage daughter Toni and a mentally unstable veteran named Jeeves. After Toni kills herself, Beau is blamed, and Grace sends Jeeves after him. Beau ends up with a traveling theater troupe that get attacked by Jeeves.

Beau eventually manages to make it home and meets his childhood love Elaine. They make love but Elaine dies mid-climax. Mona then reveals that she was alive and has always been watching Beau, making him think he's a bad son who didn't love his mom. She puts him in the attic of her home, where it is revealed that Beau's biological father is a giant penis-shaped monster that kills Jeeves when he attacks the house. After being guilt-tripped by Mona again, he appears to strangle her and tries to escape. Mona and her lawyer, Dr. Cohen, trap Beau in an arena to put him on trial and make him look guilty for being a negligent son. Beau realizes he is trapped to the boat that he tried to escape on, and he dies when the motor on the boat explodes and capsizes the boat with him stuck to it.