Molly Morris, Miley Cyrus, a private investigator based in Dallas, captures photos of cheating men. Jeremy Piven Armon Ranford interrupts one of her cases to offer a job with the FBI, and she reluctantly sees the opportunity as a means to steady her finances. She needs money to bail her gambling father, Sam Mike O'Malley, out of debt, so she agrees to join the bureau.
Undergoing a drastic makeover, Molly goes undercover as sorority sister Brook Stonebridge. She soon meets Sasha Stolezinsky, Eloise Mumford, the sorority’s head, along with Becky Kelly Osbourne, Cotton Megan Park, Hunter Morgan Calhoun, and Alex Lauren McKnight, who Molly has been hired to protect. Telling Alex they were at the same summer camp, Molly uses a small camp-specific cue to win her trust and quickly sees through the polished façades the sisters project in their bid to belong.
Her keen eye catches early signs of deception—Becky’s British mannerisms and a southern drawl, Sasha’s shrouded background, and a subtle tension around Alex’s routine. Molly also meets her love interest, Nicholas Dexter, a fellow student, Joshua Bowman. Nick and Alex recognize Molly’s detective instincts when she notes the signs of an affair as a student slips into a professor’s car.
While Alex is away, her roommate Taylor, Alexis Knapp, catches Molly snooping in Alex’s room. Molly explains she’s borrowing something, but the moment deepens the mystery of who’s genuine and who’s pretending. Ranford pushes Molly to watch for people who aren’t who they seem, which leads her to suspect Professor Talloway, Matthew Settle, and to discover that Alex sometimes goes off to Talloway’s lakeside home.
Sasha’s jealousy of Molly’s growing popularity within the sorority pushes her to plant items that have vanished from other sisters into Molly’s belongings, and the group’s dynamics begin to fracture. Ostracized, Molly asks her father to research the case, but he can’t locate much about Sasha either, driving Molly to inspect Sasha’s room herself. She uncovers that Sasha (Suzy Walters in disguise) changed her identity to escape high school shame and start fresh.
Molly keeps reporting to Ranford, who reveals that Nicholas Dexter isn’t his real name and that he’s been playing a double game. Trust frays as Molly initially believes him, and she even restrains him during a tense moment. She tracks Alex to Talloway’s home, only to learn that Talloway is in fact a federal agent, and she narrowly escapes a masked gunman—who turns out to be Ranford, fleeing with a kidnapped Alex. A wounded Talloway lies outside his cabin, complicating an already tangled web.
Back at the sorority house, two FBI agents join the effort. Skepticism gives way to belief as Morris convinces them to collaborate with the sisters to bring Ranford to justice. They execute a coordinated plan, rescue Alex, and corner Ranford, who is arrested. Alex hands over an SD card containing evidence on Sasha’s case to Molly, who passes it to the FBI.
The bureau is impressed, and Molly is offered a job with them. She declines, choosing to continue her college life instead. Two months later, Molly surveils a guy Cotton is dating, and when Nicholas and Molly reconnect, they acknowledge their dating status and share a kiss as the film ends.
