This leaves Emerald, her fun-loving brother Clovis, her neglectful and wickedly witty mother Charlotte and two servants awaiting the arrival of several friends with whom they plan to enjoy an elegant dinner party. Emerald's impish younger sister, nicknamed Smudge, sees the promised distractions of the evening as the perfect cover to action her own ambitious agenda: a Great Undertaking involving the family's pony.
The novel promises, at this point, to unfurl as an upstairs-downstairs Edwardian comedy of manners. And then the stranded passengers arrive: "... a small group of people was emerging from the gloom of the drive onto the gravel, slowly and all together. It was difficult to see how many of them there were".
The family contains the motley bunch in the morning room, throws them some tea and tries to forget about them and forge ahead with their party, assuming the railway authorities are arranging to collect them.
But there's one survivor they can't ignore, as much as they grow to wish they could. Charlie Traversham-Beechers is the sole first-class passenger, a caddish stirrer who infiltrates the family's celebration and introduces a parlour game that forces the invited guests to face unpalatable truths and reveal unsavoury character traits.
The novel gets more absurd and surreal as the night progresses. The third-class passengers begin to party - and to smell, Smudge's undertaking doesn't turn out as planned, Charlie forces Charlotte to take drastic action to get rid of him, and romance and passion bloom in unexpected places as the hosts and their invited guests put aside their differences to - at last - address the demands of the uninvited.
The result is a playful and rollicking tale, with writing that crackles with originality and wit. The supernatural element is not truly frightening and never threatens to dominate proceedings; it instead acts as a conduit for the main characters' journeys.
More unsettling than the passengers' secret is the point of view, which buzzes around like a demented blowfly, landing on one character, and then the next, sitting on the wall for a while, zooming off again... It's sometimes omniscient and sometimes limited to a certain character and by the end I found it hard to ascertain to what extent each character had figured out the truth about the uninvited guests. Thus several of the hosts and their friends seemed oddly unperturbed by the supernatural forces that have upset their plans.
That's minor gripe in what is an otherwise entertaining, witty and satisfying novel.