Being Nikki is the second book of Meg Cabot's "Airhead series" featuring Em Watts, whose brain was put into the body of supermodel Nikki Howard in the aftermath of an accident.
The novel opens with Em doing a photo shoot on a cliff in the Virgin Islands. She is clinging to a cliff at nighttime, with frigid waves lapping her legs and sharks encircling below, when she suddenly slips, falling into the shark-infested water, to be rescued by the real Nikki's on-off boyfriend Brandon Stark.
Back at the hotel, she learns that Nikki's brother Steven is phoning her because their mother has disappeared. Back in New York, she feigns amnesia to try and persuade Steven she doesn't remember anything about their mother and can't help, but Steven doesn't buy her story. Em as Nikkie promises to do what she can to help, and her roommate Lulu invites Steven to stay with them in New York.
Em approaches her best friend Christopher and his cousin Felix, because they are excellent computer hackers. They promise try and help Em as Nikki find her mother but only if Nikki gets them access to the Stark website. Christopher wants to take vengeance on Stark Enterprises because he blames the company for his best friend Em's death and still hasn't figured out Em has switched places with Nikki. During the investigation, Em also has to model in a lingerie fashion show, where she is accosted by another model and accused of messaging the other model's boyfriend, Justin.
At a party, Christopher finally realizes Nikki is really Em. Em also realizes there is a link between Justin's emails from Nikki and the disappearance of Nikki's mom. Using the emails, Christopher traces the whereabouts of Nikki's mom to just outside of New York City, in the home of Dr. Fong, the assistant to neurosurgeon Dr. Holcombe who performed the brain transplant.
The group makes its way to Dr. Fong's home where they find both Nikki's mom and the actual Nikki still alive. However, Nikki's brain has been transplanted into the body of a young woman who had died while driving drunk. Dr. Fong further reveals that, upon examining Nikki's brain, he had found that Nikki had not had an aneurism as Dr. Holcombe had claimed; Nikki's brain was perfectly healthy. So, Dr. Fong had saved Nikki by transplanting her brain into another body, albeit a much homelier person's body. It's further revealed that Robert Stark, CEO of Stark Enterprises and father of Brandon, commanded Nikki to be killed, because she was trying to blackmail Robert about some business scandal.
It's also revealed that Brandon knew all, all along. The novel ends with Brandon asking Em to help him avenge his father's actions by ruining Stark Enterprises, telling her to break up with Christopher to maintain the appearance of being Nikki, and the group going into hiding from Stark Enterprises in Brandon's island home.