Plot

Turning her back on her wealthy, established family, Diane Arbus falls in love with Lionel Sweeney, an enigmatic mentor who introduces Arbus to the marginalized people who help her become one of the most revered photographers of the twentieth century.

In 1958, in New York City, the upper class Diane Arbus is a frustrated and lonely woman with a conventional marriage with two daughters. Her husband is a photographer sponsored by the wealthy parents of Diane, and she works as his assistant. When Lionel Sweeney, a mysterious man with hypertrichosis (a.k.a. werewolf syndrome, a disease that causes excessive body hair), comes to live in the apartment in the upper floor, Diane feels a great attraction for him and is introduced to the world of freaks and marginalized people, falling in love with Lionel.—Claudio Carvalho, Rio de Janeiro, Brazil

The movie opens with Diane Arbus (Nicole Kidman) arriving to shoot pictures at a nudist colony. She is hosted by Jack Henry (Boris McGiver) & Tippa Henry (Marceline Hugot). She is asked to disrobe if she wants to take any pics.

The story then flashes back to three months earlier in New York City, 1958. Diane Arbus plays assistant to her photographer husband Allan (Ty Burrell). Diane is from a wealthy family (mother Gertrude Nemerov (Jane Alexander)); her father David Nemerov (Harris Yulin) is a furrier (he makes fur coats). Allan's family has run a photo studio for decades. Diane is clearly uncomfortable with the tepid life of a city wife and mother (to their two girls, Grace (Emmy Clarke) & Sophie (Genevieve McCarthy)).

One night during a party, she is gazing out the window and catches the eye of the mysterious neighbor who has just moved in upstairs. His face is completely covered except for the eyes and mouth. That evening after the party, Diane stands on their patio, opens her dress and exposes her bra. She admits this to her husband.

A few days later, her daughter informs her of a problem with the plumbing. Opening up a pipe, Diane discovers clumps of hair blocking it. As she removes the hair, a key tumbles down. She takes the hair and key out to the trash, and then buzzes her upstairs neighbor to ask if he's been grooming a dog. He says no, and then suggests she look in the basement, which she does. She sees an ornate chair and a sideshow poster of a "wild man," which an arm-less woman Althea (Mary Duffy) then dusts off. Diane assumes she's the wife of the neighbor. When she can't sleep, Diane grabs the camera (that her husband had gifted her years before, and she'd as of yet never used), and goes upstairs to introduce herself to her neighbor, and ask if she could shoot his portrait. He asks her if she got the key, and then tells her to return the next night. She leaves, and then goes to grab the key out of the trash.

Thus begins her relationship with Lionel Sweeney (Robert Downey Jr.), a man with Hypertrichosis who is in demand as a wig-maker. He shows her videos of how he was treated like a circus freak due to his condition. All around the apartment, Diane sees photos of similar "freaks" who suffered from some physical deformity or the other, and hence were treated as outcasts by the society. The first interaction focuses on Lionel trying to question Diane about her repressed sexual fantasies (like with the hired help in her parents' house, while she was growing up).She talks about a boy with a purple birthmark, who ran away before she could speak with him. She tells Lionel about her desire to visit the morgue, doll hospital, dump, flophouses and other places where normal girls would never like to go. They have a bath together.

Lionel sees in Diane a kindred spirit, and he takes her places where she meets transvestites, dwarfs and others living on the fringes of society. Diane tells Allan she'd like to take time off from the business to take her own photographs, starting with the neighbors. He's supportive of her. As Diane spends more with Lionel, she grows more attracted to him and this new, strange and exciting world. She's taking photographs but hides the undeveloped film in a cookie jar. The key was to Lionel's apartment, so Diane can let herself in at any time.

Lionel asks to be introduced to Diane's husband. Soon Diane has brought Lionel even into her family life. Her children help him with his wig making business, and he reads bedtime stories to them. She introduces him to her mother and father. At her and Allan's anniversary party, Diane finds Lionel breathing in some substance. He admits that his lungs are disintegrating, and within a few months he'll be "drowning." She cries at this news. They almost kiss, but are interrupted by Allan, who sees their intimate moment, and then leaves. Later at home, he asks Diane if she'd kissed him, but then realizes it doesn't matter if they have or if they haven't, that he knows her feelings towards Lionel. He begs her not to tear their family apart. Diane agrees to end the affair and dresses and goes upstairs to do so.

When she lets herself in to Lionel's, she finds him naked with shaving cream and razor in hand. He asks her to completely shave him. When he's naked, they make love. When she asks why he wanted to be shaved (after previously professing it wasn't worth the effort), he reveals he intends to "swim out," to commit suicide in the ocean, and wants her to be with him when he does it. She's devastated but agrees. They profess their love for each other. In the meantime, her daughter, having found her film stash, gives it to Allan to develop. Allan sees his wife's talent for the first time.

At the beach, Lionel presents Diane with a gift: a fur jacket, made from his own hair. She walks with Lionel to the edge of the water, and watches as he gleefully swims out.

She returns to her home, and as she puts the key in the door, realizes she cannot go in, back to her old life. Allan, standing on the other side of the door, does nothing. Diane returns to Lionel's apartment, rolls in his bed, and breathes the air he'd blown into a life raft to inflate it. Suddenly, she's surrounded by all of Lionel's friends, and they have a party to honor him. One of his friends gives her a photo album Lionel wanted her to have. It has fifty empty pages, all with photo plate tags in Lionel's handwriting. He wants her to fill them with her photographs.

Diane, touched by her experience with Lionel, now knows what direction to take with her life and career. The final scene shows her at a nudist camp, where she meets a woman who assumes she wants to take her picture. Arbus admits this, but first asks the woman to tell her a secret. The woman asks Diane to tell her a secret first, and Diane agrees.