Dark Circle by Linda Grant

The Second World War is over, a new decade is beginning but for an East End teenage brother and sister living on the edge of the law, life has been suspended. Sent away to a tuberculosis sanatorium in Kent to learn the way of the patient, they find themselves in the company of army and air force officers, a car salesman, a young university graduate, a mysterious German woman, a member of the aristocracy and an American merchant seaman. They discover that a cure is tantalisingly just out of reach and only by inciting wholesale rebellion can freedom be snatched.