The first one was Marissa. One day, she went out on the surface. She took off her air mask, not knowing there was a crack in it. The removing of her mask caused the crack to widen, and the pressure of the oxygen escaping from the tank pushed her down a slope of sharp rocks.
Jovain Pallis had been in love with Marissa, but she didn't return his affections, so he thinks that her death has some advantages for him.
As Jovain and Isabel de Veigh work in the air room, she breaks down crying, blaming herself for Marissa's death. Jovain tries to make her feel better.
Then, a stranger, called the Doctor, arrives. The colonists accept him without questioning, assuming that he arrived in some kind of spaceship. He asks questions and examines tanks in the air room.
Isabel tells Jovain that the murders must have been one of them. They are the only two who work regularly in the air room. Suddenly, the Doctor is there. He explains the motives for the deaths. Jovain killed Marissa because he couldn't have her. He knew Isabel suspected him, so he tried to kill her, but Uther grabbed her tank instead, and was killed.
The Doctor sees that Jovain has no remorse for his crimes. He takes Jovain to an uninhabited planet and leaves him there to live out the rest of his life, away from everyone else.
- The colony was originally going to extract titanium from the crust, but it is cheaper to get it from the Moon.
- The stories in Short Trips: Steel Skies are divided into four sections dealing with different types of confinement. This story deals with frontiers, that is, "the corridors, living quarters and ventilation shafts of four futuristic environments".
- This story is narrated by Jovain Pallis.
to be added