Moebius

On 4 March, the Buenos Aires Underground discovers that train UM-86 and its passengers have disappeared from the network. A comprehensive search of the tunnels is launched, but neither the train nor its occupants are found. The network is shown as far larger on screen than in reality, complicating the search.

To conceal the incident from the public, the director of SBASE reaches out to the engineering firm responsible for the line to initiate an investigation. The firm sends Daniel Pratt, a young topologist, rather than a veteran engineer, which displeases the director. Pratt begins the assignment while the rest of the team remains skeptical.

Pratt attempts to locate the original plans for the line at a national archive, only to learn they are missing. He discovers the plans were taken by his former lecturer, Hugo Mistein. The professor is nowhere to be found, retired and out of contact.

Pratt traces Mistein's address and, because he has little change, calls from a public phone. When Pratt arrives at the apartment, he is greeted by a reluctant young girl who lets him in. They realize the missing plans are inside, but they must escape through the fire exit when a knock on the door interrupts them.

Inside a station, Pratt and the girl join the authorities to locate UM-86 and the missing passengers. The entire line has been shut down to simplify the search. A train sound is heard through the tunnels, and the director orders the power cut, which only angers the committee.

Pratt presents his Möbius strip theory, arguing that the network's construction has turned the tunnels into a loop that could channel UM-86 into another dimension. The idea is ridiculed by the committee, and Pratt is relieved of his post as investigator. He leaves the station with the girl.

After seeing a roller coaster at Parque de la Ciudad, Pratt is inspired to perform a series of mathematical calculations to test his theory. He returns to the underground line and starts taking notes on train movements and schedules. He realizes that UM-86 is due to reappear according to his calculations.

Pratt studies the timetable and movements across the network, compiling data throughout the day. He deduces a pattern that implies UM-86 will materialize again under certain conditions. His persistence leads him deeper into the tunnels as he tracks train activity.

Pratt enters maintenance passages and ascends a level, nearly colliding with an arriving train. He continues through maintenance areas until he emerges at another station named Borges, a deliberate director's choice.

On the Borges Station-bound train, Pratt boards the first arriving train and discovers UM-86, with its 30 passengers in a tranquil trance. In the conductor's cabin, he finds Hugo Mistein waiting for him, leading to a philosophical discussion that corroborates Pratt's theory.

The following day, the director is summoned to a station and finds UM-86 empty of passengers, with Pratt's journal left in the conductor's cabin explaining the theory. The discovery leaves the director unsettled and raises questions about Pratt's explanation.

As the director is about to depart, he receives a telephone call reporting another missing train, signaling that the mystery is far from resolved. The call hints at a broader phenomenon tied to the same network riddle.