The nation is on the road to recovery after World War Two. And so is Milly Hendry.

When her parents were killed in the Blitz, she was taken in by her aunt who works in the prestigious Royal Army of Cleaners. Buckingham Palace has since become like home to Milly, and the people she works with like family.

Though tensions in the palace are rising as the King's health is declining, the staff gather below-stairs to celebrate Milly's 21st birthday. But her day quickly takes a turn when some unexpected post arrives.

Could a letter containing secrets from the past change Milly's whole future?