When her parents accept summer teaching jobs in Rome, talented, troublemaking, twelve-year-old Mia Moretti tags along. Eager to learn more about her surroundings, she drags her new friend, buttoned-up-and straight-laced Grace, out to explore the Italian cityscape. But when they stumble upon a strange street carnival, Mia wins a mysterious prize: a fragment of a bone from an ancient conjuror secured in a velvet pouch and strung on a necklace. Supposedly, it makes the wearer lucky in anything they attempt until nightfall.

Sensing danger, Mia throws the bone into the dumpster. But the carnival disappears into thin air, and the bone mysteriously finds its way back to them. The only way to rid themselves of it is to reunite it with the decaying skeleton it came from before the sun sets.

But by the time they locate the remains and attempt to return the bone, they're too late. Caught between life and death and trapped inside the nightmarish carnival, they discover an alarming plot that threatens more lives than just their own. Mia and Grace team up with another recently-taken boy, Val, and the three of them must get their souls back into their bodies in Rome, or else their spirits will be imprisoned for all eternity.