The Runaway Summer — Nina Bawden

Deeply unhappy at the recent divorce of her parents, Mary is sent away to live by the sea with her distant grandfather and the detestable Aunt Alice. Feeling abandoned, without even the company of her beloved pet cat Noakes, the summer looks set to become one long stretch of unendurable loneliness. But suddenly she is dragged, half unwittingly, into a situation that will force her to come to the aid of others more vulnerable than herself. So begins her runaway summer, as she sets about helping Simon, the son of a local policeman, and a young illegal immigrant boy arrived from Kenya, frightened and all alone.
The Runaway Summer was first published in 1969 to typically universal acclaim. It is, in the words of the Times Educational Supplement, an 'unputdownable gem of a book. The tale is beautifully constructed in diamond-hard language.'