England, 1930s. Christopher Banks has become the country's most celebrated detective, his cases the talk of London society. Yet one unsolved crime has always haunted him: the mysterious disappearance of his parents, in Old Shanghai, when he was a small boy. Now, as the world lurches towards total war, Banks realises that the time has come for him to return to the city of his childhood and at last solve the mystery - that only by his doing so will civilization be saved from the approaching catastrophe.