Walking to Aldebaran

Astronaut Gary Rendell is trapped in a labyrinth. He has been alone for an unknown period of time, possibly for months. As a result, he is experiencing paranoia and dissociation. He narrates his story to a figment of his imagination, whom he calls "Toto".

In a series of flashbacks, Rendell recounts how a space probe discovers a Trans-Neptunian Object of alien origin. This Artefact is a massive circular object full of holes of varying sizes. Further investigations reveal that these are tunnels which can connect to other solar systems.

Rendell is selected as one of the first human explorers to investigate the Artefact. After several years of spaceflight, Rendell and his crew reach the Artefact. While many of the tunnels are inimicable to human survival, the team identifies one area with the correct atmospheric pressure, gravity, and oxygenation for a crewed mission. Rendell and the other explorers are sent inside the Artefact.

The team of six astronauts journeys into a labyrinth, which Rendell calls "the Crypts". They are ambushed by a local predator. Four astronauts are killed outright, and Rendell is separated from the only other survivor. Rendell wanders through the Crypts for several days. Weak and hungry, he encounters a structure which he calls the mother machine. The machine swallows Rendell, tearing him apart and remaking him at a cellular level. As a result of these modifications, he will never starve or suffocate in the harsh environments of the Crypts.

As he continues to wander, Rendell encounters several other sentient species. Some, such as a group of metallic eggs, appear friendly. Others are aggressive; he kills a worm-like creature that attacks him. The Crypts contain many dangerous environments, including areas where gravity changes unexpectedly. The loneliness and constant threats begin to wear on Rendell's mind. Rendell begins hearing a "scritching" noise in his mind and becomes convinced that an alien creature is transmitting signals into his brain.

Rendell finds a humanoid creature which he dubs the "iron hunchback". It attempts to speak to him in Dutch and hands him a food wrapper, indicating it has had contact with humans. Rendell attacks the creature and chases it off. Rendell encounters a group of smaller creatures, which he calls goblins. He suspects they may be causing the scritching. Toto tells him to kill them all. Rendell kills the goblins and begins to eat them. The goblins are revealed to be human explorers. Even after realizing their true identities, Rendell continues to hunt the surviving humans. The scritching sound is revealed to be a result of the mother machine's alterations, as Rendell has gained the ability to sense human thoughts.

Rendell finds the exit from the labyrinth, bringing him back to where his journey began. He attacks a group of humans, but they are defended by the iron hunchback. The creature severely injures Rendell by tearing off his arm. Rendell flees back into the Crypts. He cries out to the mother machine for help as he dies.