Mars, which has become a place where sufferers of blood rust are exiled.
Saul Williams - An exile on Mars dying from blood rust.
Leonard Mark - Telepath gifted with the ability to create lifelike experiences.
Man on blanket - Another exile.
Two men on rocket - Deliver Leonard Mark to Mars.
Smith - One of the exiles who negotiates for access to Mark.
Peter - One of the exiles who negotiates for access to Mark.
Johnson - One of the exiles who negotiates for access to Mark and also has a gun.
Holtzman - One of the exiles who negotiates for access to Mark.
Jim - One of the exiles who negotiates for access to Mark.
Saul Williams, who is dying of loneliness and intellectual deprivation - as well as the disease blood rust --on Mars.
Leonard Mark, who has the ability to create lifelike illusions.
In a struggle for control of Leonard Mark, Saul and five other exiles shoot Mark and kill him.
Saul is again lonely and deprived.
The main themes are the struggle for sanity in an insane situation and the dangerous power of the creative imagination. The isolation of the exiles in the story has stripped not only their humanity but their ability to productively imagine, which is what makes Mark so valuable.
Saul Williams is an exiled Earthian living on Mars, suffering from blood rust. He wishes to be back on Earth, in New York City, and is bereft of hope. He wishes to die, suffering deeply from loneliness. One of the other exiles, a man on a blanket, assures Saul that all the rusted ones suffer from this loneliness. Saul desires intellectual discussion, but as the disease takes its toll all a person cares for is sleep and whatever solace it provides.
Saul leaves this man behind and watches as a rocket lands with a new exile. The young man's name is Leonard Mark and when Saul greets him, asking how things are in New York, Leonard shows him: Saul is overwhelmed by the sights and sounds and smells of New York, believing he's gone crazy. In actuality, it is Mark's strange ability to conjure such experiences through telepathy and thought transference, an ability that probably resulted from his being born soon after the London blowup of 1957. Saul asks to skinny-dip in a creek he knew as a child, and Mark indulges him. Saul tries to repay him with his last bar of chocolate, but Leonard refuses. Saul feels lucky at this new friendship and all it means, but is also concerned about the other exiles who'll also want access to Mark's abilities. Indeed, he sees a crowd of them approaching and tries to convince him they both should flee; Mark scoffs at this, but Saul becomes possessive and knocks out Mark to take him away.
Hidden away in a cave with his friend / kidnapper, Mark uses his power to scare Saul, then to try to hide from him. Neither works, but five other men arrive at the cave. Mark welcomes them and all six discuss how to handle the matter: Mark proposes appointments for each person, with Saul on probation for bad behavior. One of the men, Johnson, asks why they can't simply force Mark to perform for them at will. Mark protests, but it's futile - he reveals that he's read their minds and knows one of them has a gun. He uses his powers to try to escape from them but Johnson pulls out his gun and fires it several times, killing Mark in the process. Saul is disgusted with himself and the others, leaving them to handle the burial. He tries to imagine New York City on his own but is unable to do so, and cries in his sleep.
The exiling of people with fatally contagious illnesses has happened historically, such as the leper colonies on the Hawaiian island of Molokai.