Betsy Bow-Linnet is determined to become a world famous concert pianist like her parents. There's just one problem: no matter how hard she practises she doesn't share their musical talents. So when a mysterious letter arrives from a woman claiming to know of an unusual method that will make Betsy's playing stupendous, Betsy jumps at the chance. There's just one condition: she must keep the method a secret. But it isn't just one secret⁠—it's forty-four tiny secrets in the shape of a boxful of pygmy mice! Betsy is mystified how are they going to help her play the piano and more importantly how on earth can she keep them all a secret?