Eleven-year-old Molly Moon is known and loved for her incredible powers - hypnotism, time travelling, mind reading . . . But now something seems to have power over her. Not only has it made her a brilliant musician, it's given her thousands of new fans, all of whom are mesmerized by her.

Literally. Only Petula, her pet pug, senses an off-note. Molly-the-Maker-of-Magical-Music is one thing, but Molly-the-Big-Old-Meanie is another - and every day Petula sees her kind owner become more and more horrible.

What is going on? And can one determined dog sort it out . . . before Molly becomes truly monstrous?