What is the theme in The Death of the Heart by Elizabeth Bowen?

The outsider is a theme in this story. Anna and Thomas Quayne live in an insular world, comfortable knowing what will happen from one day to the next. Into their lives comes Portia, the daughter of Thomas' father and his mistress (later his second wife), Irene. Portia's very presence is a source of discomfort to the couple, and she enters their house as the consummate outsider. She is an orphaned love child in a childless household where two miscarriages have occurred. Even before she came to London, Portia was an outsider, banned to the continent by her father's first wife, doomed to wander from cheap hotel to cheap hotel.