Scarlet and Ivy return to creepy Rookwood School for a third mystery adventure! With their evil headmaster, Mr Bartholomew, safely out of the picture and kindly Mrs Knight in charge, it looks like life at Rookwood School is looking up. There's a ballet recital Scarlet is desperate to star in, and more clues to uncover about the twins' mother. But after their beloved ballet teacher Miss Finch suddenly disappears and strange Madame Zelda takes her place, freakish things start happening. Poison-pen letters are circulating the school, and 'accidents' are plaguing the students. It seems that the girls are in danger once more… Is someone out for the ultimate revenge?