Callie brings her shy younger sister, Elise, to their first day at theater camp. Elise, uncomfortable and self-conscious, wears a mask to hide her face. Callie promises to support Elise and encourages her to participate. Despite this, Elise struggles with insecurity, fearing people will judge her appearance, especially when performing.

Throughout the camp, Callie becomes jealous of Elise’s natural beauty and talents. Elise starts to get attention from their peers, including a boy named Danny, whom Callie has a crush on. Callie’s jealousy leads her to cruelly pressure Elise into wearing the mask and belittling her appearance. However, their mother overhears one of Callie’s mean comments and confronts her, teaching her an important lesson: the sun and the moon both shine in their own unique ways, and there’s no need for comparison.

Realizing her mistake, Callie apologizes to Elise, admitting that her jealousy was behind her behavior. She acknowledges Elise's beauty and talents, but also learns to appreciate her own strengths. In the end, both sisters succeed—Callie gets a callback for a major role, and Elise is praised for her natural talent. They both learn that they can shine together without competing for the spotlight.