Two teenage girls in suburban Connecticut rekindle their unlikely friendship after years of growing apart. In the process, they learn that neither is what she seems to be, and that a murder might solve both of their problems.
In suburban Connecticut, upper-class high schooler Amanda euthanizes her crippled horse with a knife, resulting in charges of animal cruelty.
Some time later, Amanda arrives at the home of the more popular and academically inclined Lily. The girls had previously been best friends but grew apart after the death of Lily’s father. They meet under the pretense of hanging out and having a casual tutoring session, but it is quickly revealed that Amanda’s mother has paid Lily to socialize with Amanda, worried about her daughter after the death of her horse. Embarrassed, Lily denies being paid, but Amanda, left emotionless by an unspecified mental disorder, is unfazed. Lily meets with Amanda again, this time voluntarily, and they rekindle their friendship.
Lily lives with her mother and stepfather, Mark, a wealthy but vain and cruel man whom she hates. One night, after discussing Amanda’s techniques of feigning emotion to appear normal, Amanda asks if Lily ever thought about killing Mark, upsetting Lily. However, tensions flare between Lily and Mark when Mark enrolls Lily, who was expelled from her previous school for plagiarism, in a boarding school for girls with behavioral issues. After then seeing him berate her mother, Lily reconsiders and calls Amanda about the notion of killing him. She proposes that Amanda perform the murder as she, unlike Lily, would be free of guilt while doing it. However, Amanda believes that her pending animal cruelty trial would make her an immediate suspect, and they decide instead to blackmail ambitious but pathetic drug dealer Tim into murdering Mark while both Lily and Amanda are out of town with airtight alibis. The night of the planned murder, however, Tim arrives on the property but leaves without killing Mark. The girls agree not to contact Tim again, as his own criminal history would prevent him from reporting the girls to the police. Lily impulsively prepares to kill Mark herself but is talked out of it by Amanda. In an argument, Lily begs Mark to leave her mother. In response, Mark accuses Lily of being self-centered and reveals that he will no longer provide financial support after she completes her academic year at her new school…