The presumed death of Harriet de Luce in a mysterious mountaineering accident in Tibet while Flavia was only a baby cast a sombre shadow over the family, leaving Colonel de Luce a broken man and Flavia herself with no memories of her mother.

But now, astonishingly, a specially commissioned train is bringing Harriet back to Buckshaw. But rather than putting the past finally to rest, Harriet's return is set to trigger a further series of bizarre and deadly events, as a most curious group of individuals converge on Buckshaw to pay their respects.

For Flavia, a gruesome new crime to solve is only one of the mysteries confronting her, as she begins to unravel the shocking revelations of Harriet's past and in doing so discovers an extraordinary tale of espionage and betrayal that also seems to be the key to her own destiny.