The Morning Gift book by Eva Ibbotson

Ruth lives in the beautiful city of Vienna and is wildly in love with Heini Radik, a brilliant young pianist. But her world is about to change forever. When Hitler's forces invade Ruth's family flees to London, but she is unable to get a passport. Quin, a young professor and friend of the family, visits Ruth and in an effort to bring her back to London, he offers a marriage of convenience. As Ruth throws herself into her London life, Quin begins to fall desperately in love with her. Things are further complicated by the arrival of Heini...