Caraval (Caraval Series, Book 1)

Scarlett has never left the tiny isle of Trisda, pining from afar for the wonder of Caraval, a once-a-year week-long performance where the audience participates in the show.
Caraval is Magic. Mystery. Adventure. And for Scarlett and her beloved sister, Tella, it represents freedom and an escape from their ruthless, abusive father. When the sisters' long-awaited invitations to Caraval finally arrive, it seems their dreams have come true. But no sooner have they arrived than Tella vanishes, kidnapped by the show's mastermind organiser, Legend.
Scarlett has been told that everything that happens during Caraval is only an elaborate performance. But nonetheless she quickly becomes enmeshed in a dangerous game of love, magic, and heartbreak. And real or not, she must find Tella before the game is over, and her sister disappears forever.