Be Frank With Me, by Julia Claiborne Johnson

This gripping and unusual tale of a nine-year-old genius conjures up the ghosts of Harper Lee and J D Salinger. Wunderkind author Mimi Banning has lived in Californian seclusion for decades, ducking the fanatics inspired by her debut novel. She needs to write a much-belated second novel to escape financial trouble after being defrauded. Her long-suffering New York publisher drafts his capable assistant, Alice, to monitor her progress and remove any impediment to completion. Alice can’t get a look at Mimi’s manuscript and finds herself acting as housekeeper and nanny to Mimi’s eccentric nine-year-old son, Frank. Families are strange beasts and practical Alice navigates many twists and turns in her quest to solve the mystery of Frank and his family, learning a lot about herself in the process.