Sierra Burgess is a smart and witty teenager who attends the same high school as Veronica, the most popular girl in school. One day, Veronica gives Sierra's phone number to a boy named Jamey, thinking it's hers. Sierra realizes that Jamey thinks he is texting Veronica, and starts to text him back pretending to be her.
Over time, Sierra and Jamey develop a connection through text messages and phone calls, but Sierra is too scared to reveal her true identity. Meanwhile, Sierra's best friend Dan encourages her to be more confident and to embrace her unique qualities.
As Sierra and Jamey's relationship starts to grow, Veronica begins to feel guilty about what she has done and starts to sympathize with Sierra. The two girls form an unlikely friendship and work together to win Jamey's heart.
Sierra creates a plan to finally reveal her true identity to Jamey, but things don't go according to plan and she ends up hurting him in the process. However, with Veronica’s help, Sierra finds a way to make things right and win back Jamey's affection.
The movie showcases the importance of self-love and acceptance, and how a person's true qualities and personality can shine through regardless of who they are on the outside.