Jack has always known his little sister, Annie, is bright.
By the time she's five, she's reading Hamlet and the Financial Times, and has an extremely active imagination.
Her odd behaviour doesn't make life easy at school for Jack, especially when Annie insists that she has an invisible but very real friend called Sarah, who accompanies her everywhere.
Jack is desperate to prevent Annie's obsession causing problems at school - good behaviour is vital if they're to be allowed to go on the long-promised trip to America to meet their absent father.
When they are finally aboard the plane for America, Jack is thinking quietly, maybe drifting off to sleep, when he is rudely interrupted by the crystal clear voice of a girl - not Annie, but Sarah!
A perceptive, amusing and moving novel about sibling relationships, absent parents and the borderline between truth and imagination, which will be eagerly enjoyed by boys and girls of 8+.