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 a 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?