Gray captures cleverly the horror of the plain, book-gobbling child being born into a celebrity family, without any knowledge of her pa, the star at its centre. Much of the story takes the form of a mystery in which Ada catches glimpses of her father from those who knew him. Her mother refuses to discuss him in detail, even after his death (until a theatrical reveal at the end). Gray gives us a basic maths tutorial along the way, but, appropriately for youngish readers, the details of Ada’s discoveries play second fiddle to her upbringing...