When troublemaking Scarlet vanishes from Rookwood boarding school, Ivy, her quiet twin sister, is invited to "take her place." But when Ivy arrives, she discovers the school's true intention. She is not simply taking up Scarlet's enrollment. She must think like Scarlet, act like Scarlet, become Scarlet. What on earth happened to the real Scarlet, and why is the school trying to keep it a secret? Through a scattered trail of diary pages carefully hidden all over the school by Scarlet, Ivy must figure out what happened to her sister before it's too late.