Dick, an astronaut in the 21st century and one of the first men on Mars, is relating his experience meeting an ostrich-like alien to his disbelieving and somewhat-hostile crewmates. Assigned to a scouting ship to take pictures of the planet, the engines cut out and Dick crashes 800 miles away from the landing site near an abandoned city. Since there is breathable air and some strange plants around, Dick decides to walk back to the main ship instead of wait to be picked up. Along the way, he comes across an ostrich-like alien named Tweel getting eaten alive by some strange tentacled monster. After shooting the monster and saving Tweel, the two travel together. Communication is mostly futile as Tweel speaks in chirps, but when Dick draws a rudimentary solar system and points out how he is from Earth, Tweel grows excited and leaps high into the air before landing on his beak dead in the center of the sun.

Over their next few days of walking, across the Martian desert, the two see strange objects like floating, clear, ball-shaped tumbleweeds and tiny stone pyramids. The pyramids grow in size until they are as tall as a human and suddenly a strange grey lump of an alien pops out. After analyzing them for a bit, Dick realized that they were a silicon-based life form. The pyramid blocks were its waste matter and the tumbleweeds were its attempt at procreation. As the land they're standing on is silicon rich, the creature could consume the soil and over long periods of time, which produces these bricks that it can lay out as a home. Dick notices that the creature is not sentient, contrasting heavily with the personality and intelligence of the ostrich-like Tweel.

Later that night, Dick and Tweel see an apparition of a woman Dick knew from Earth. Tweel stops him from approaching her and after snapping out of the hallucination, Dick sees that it is actually another of the rope-like creatures that he saved Tweel from earlier. The crew is skeptical of Tweel's intelligence, but Dick stands up for it, saying that Tweel is just as smart as any man there. Dick uses his experience with a final group of aliens that build cities from mud as proof. These aliens have many eyes and limbs, the ability to speak, and working electricity and machines, but according to Dick they lack any real higher order thinking since all they do is parrot back things they hear and perform a series of rote tasks before promptly killing themselves. The aliens suddenly turn on Dick and Tweel and begin attacking them. The pair are saved at the last moment by one of the crewmates appearing with a rocket and crushing all of the aliens underneath it. Tweel leaps away, never to be seen again, and Dick reveals that he had stolen away a powerful healing crystal from the non-sentient aliens, explaining why they attacked him.