It was another ride on another train, oh Agatha and trains is like Spielberg and bicycles! Well it was a good ride, with good characters and interesting twists. The mysterious Comte de la Roche trying to mess everything up. The dancer, the war vet, the rebel, the dead wife, the enigmatic M. Papopolous and his daughter. Then there is the mysterious Marque. All ties together in such a way that you find yourself turning in every other direction. It was also the first novel in which Agatha used supernatural aspects to deliver a twist. Her writing style incorporated more variety and it was a fun read!
You might also be hard pressed to read a book first published in 1928 that reads like a modern thriller! The Mystery of the Blue Train.