In 1936, diplomat Sir Hallam Holland and his wife Lady Agnes move into 165 Eaton Place and launch a new era for the sumptuous home at the heart of Upstairs Downstairs.

October, 1906. During a week when Richard Bellamy is alone in the house, working on a book, he finds the young under - housemaid, Mary, crying as she lays the library fire. He learns of her secret ...

Downstairs regulars Hudson, Rose and Mrs Bridges are joined by a troublesome new chambermaid.