Eleven-year-old stuttering Darby believes she's supposed to be perfect, just like her mother demands. But summer away at camp promises temporary escape. There, she befriends Justin, who hasn’t uttered a word since his dad died, and Naz, who is struggling to learn English.
When mysterious calliope music from a nearby warehouse grants the trio power to communicate without words, they sneak inside to find out why. After the abandoned building bursts into a full-sized carnival with magical rides, they're greeted by the ghost of Leroy Usher, Carnival King, who can’t rest until his property brings joy to children once again.
He asks for their help convincing his estranged sons and daughter to restore the carnival to its former glory before summer's end. In return, Mr. Usher promises he'll teach Darby, Justin, and Naz how to find their voices.
Using an enchanted pocket watch, he sweeps them off on a series of midnight adventures. As the kids learn they're capable of accomplishing more than they ever imagined, they scheme to persuade the Usher siblings to bring the carnival back to life instead of selling the property to developers.
With each challenge they face, their confidence in communicating—and in themselves—grows. But when Darby’s bunkmates trick her into a taking a starring role in the camp's talent show, her budding confidence falters. If she can't risk being less than perfect by performing in the talent show and speaking up to Mr. Usher's resistant son, she'll put the carnival in danger and sabotage her most important quest—to believe in herself, stutter and all.