Ninety-one-year-old Gretel Fernsby has lived in the same mansion block in London for decades.

She leads a comfortable, quiet life, despite her dark and disturbing past. She doesn't talk about her escape from Germany over seventy years before. She doesn't talk about the post-war years in France with her mother.

Most of all, she doesn't talk about her father, the commandant of one of the most notorious Nazi concentration camps.

Then, a young family moves into the apartment below her. In spite of herself, Gretel can't help but begin a friendship with the little boy, Henry, though his presence brings back memories she would rather forget. One night, she witnesses a violent argument between Henry's mother and his domineering father, one that threatens Gretel's hard-won, self-contained existence.

Gretel is faced with a chance to expiate her guilt, grief and remorse and act to save a young boy - for the second time in her life.

But to do so, she will be forced to reveal her true identity to the world. Will she make a different choice this time, whatever the cost to herself?