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When her young daughter starts behaving strangely, a fertility doctor who believes firmly in life and death must challenge her own values and confront a ghost from her past.

As a fertility doctor, Sarah has a firm understanding of the cycle of life. However, when she is forced to make sense of the increasingly strange behavior of her young daughter, Sarah must challenge her own beliefs and confront a ghost from her past.—Official Synopsis

Fertility doctor Sarah begins her beloved daughter Mia's seventh birthday expecting nothing amiss. But as an ominous wind swirls in, Sarah's carefully controlled world begins to alter. Mia begins behaving oddly and a rabbit appears outside their front door - a mysterious birthday gift that delights Mia but seems to deeply disconcert Sarah. As days pass, Mia becomes increasingly not herself, demanding to see Sarah's long-estranged, hospitalized mother (the grandmother she's never met before) and fraying Sarah's nerves as the child's bizarre tantrums begin to point her toward Sarah's own dark history. As a ghost from her past re-enters Sarah's life, she struggles to cling to her distant young daughter.—Sundance Film Festival

Sarah, a divorced fertility doctor, celebrates her daughter Mia's seventh birthday. The pair find a rabbit at their house, which Mia grows attached to. The night of Mia's birthday, they are joined by Peter, Mia's father; Denise, Peter's new partner, and Toby, Denise's three-year-old son. While playing, Mia screams when Toby hits her on the head. Sarah angrily rebukes Toby and Denise, but Peter smooths things over. Later at night, Sarah attempts to send the rabbit over their garden wall, but it bites her. Sarah realises that Mia saw her try to get rid of the rabbit.

Starting the next morning, Mia's behaviour grows strange. She becomes intermittently unresponsive, and starts wearing a self-made rabbit mask that she refuses to take off when Sarah asks. At school, Mia hides in a playground tube in fear, but denies that she's being bullied. Mia says she misses her grandmother, Joan, whom Sarah is estranged from and whom Mia has never met.

When Mia asks for family photos to make a family tree, Sarah finds a childhood photo of herself and her younger sister; Mia claims to be in the photo. While Mia's behaviour becomes more erratic, Sarah starts hallucinating, her nightmares grow more intense, and the rabbit bite on her hand becomes infected.

Due to Mia's insistence on seeing Joan, Sarah takes her to visit the assisted living home where she lives. Joan, who has dementia, refers to Mia as "Alice", which Mia reacts strongly to. Sarah forcefully separates the two, and injures Mia's hand when trying to control her. Afterward, Sarah hurts her own hand to mirror the injury. Sarah learns from Mia's schoolteacher that there are disturbing drawings on the underside of Mia's homework, and Sarah realises that all of Mia's artwork at home has similar drawings.

Sarah questions Mia about her behaviour, and Mia declares that she is Alice. At Peter's suggestion, Sarah takes Mia to Sarah's childhood home, and tells her about her sister Alice, who went missing when Alice was seven. Sarah is angered when Mia continues to say that she is Alice, and claims that Sarah bullied her. Sarah's hallucinations worsen, and she unintentionally cuts Mia with scissors.

Sarah hallucinates her childhood memory of Alice, confusing her sister with Mia. As a child, Sarah locked Alice in the shed; after Sarah released her, Alice choked her, Sarah hit her head with a steel trap, and when Alice started screaming, Sarah pushed her off the cliff to her death.

Peter arrives at the house, where the family photos have been smashed and Sarah has been drawing on the floor in a fugue state. The pair search for Mia, all while Sarah is hallucinating about Alice drowning. They find her in a bush. Sarah goes to the nursing home to talk to her mother, Joan, and admit Alice is dead. She goes back to her childhood home and apologises to Mia/Alice, that she hurt Alice and lied about Alice running away. Mia calls her a monster. The next morning, Sarah searches for Mia and, looking out the window, sees Mia and Alice holding hands while walking to the cliff. (thanks to Wikipedia)