The story is set beneath Buenos Aires, deep within its labyrinthine subway system, and centers on a train containing 30 riders that has mysteriously disappeared. The subway officials are greatly troubled and so call in topographer Daniel Pratt to help them find it. Unfortunately, the tunnel system is so vast and complex, that Pratt must find his mentor Hugo Mistein for help. Unfortunately, he too has disappeared. Fortunately, he left the system plans behind and as Daniel studies them, he comes to the awful realization that the train, which can be heard but not seen, has somehow become trapped in a fourth dimension. His findings attract the attention of local bureaucrats who are too rigid and pragmatic to accept Pratt's outlandish theory.