The passengers riding the train remember nothing of their lives from before they were put aboard. They have no idea where the train is going. In fact, they argue whether the landscape they see through the windows is real or just their imagination. They discuss the nature of the Engineer who drives this train, believing him omniscient and almighty. And they wonder what will happen to them when some day, unexpectedly, a Conductor tells them, "Your ticket has expired," and throws them off the train, out into whatever exists outside, or perhaps into nonexistence. And then one day a woman is put on board who, by some mistake, remembers fragments of her life from before. In shock and horror, the passengers brand her as a heretic, someone who must at all costs be stopped. Later, a dangerous expedition begins, avoiding the everpresent Conductors, and hoping to reach the head of the train and find out from the all-powerful Engineer where they are going and what is going to happen to them when they are forced off the train - and what they can do to change the inevitable.