When Arch turns up at St Grizzle's, Dani is delighted to introduce her best friend to her new classmates. But she soon discovers that mixing her old life with her new one isn't quite as easy as she'd imagined. And Arch isn't the only new pupil - there's also super-smart Boudicca, who barely says a word to anyone. It's only when she meets Arch that she perks up and takes to following him everywhere he goes. Then she disappears. With the help of Granny Viv, it's up to Dani and Arch to find Boudicca ... and unravel the truth about this shy tag-along zombie.