The guard, who talks briefly with the first convict at the beginning of the play as the latter, expecting to face execution any day, paces back and forth in his cell nervously.
The prison doctor, who is respectful of the first convict’s scientific knowledge and accomplishments in medicine, although he does not believe the latter’s story about his wife’s collusion with the defense attorney.
The warden, who visits the first convict twice (in act 1) to announce that his wife has come to see him and then that he may have a reprieve from his death sentence if he agrees to a proposal by the representative of a scientific agency. As a condition of accepting the proposal, the first convict is thereafter not allowed to see his wife.
The representative of a scientific agency, who comes to the first convict with a top secret proposal, a scientific experiment involving a manned rocket being sent into outer space with little chance of the men on board returning or surviving the journey. The first convict agrees to participate in the experiment as preferable to his imminent execution.
The second convict, the first convict’s companion on the rocket (in act 3), an engineer specializing in electrical and atomic sciences. He too feels that death on the rocket is preferable to death on Earth. He had been sentenced to death for the murder of four older wealthy wives after being caught planning to do the same with a fifth wife. He married all of them to obtain money to finance a beneficial engineering project. He also does not believe the first convict’s story about his wife’s collusion with the defense attorney. On the strange planet, the second convict worries about a life without work, events, and a future, and he suggests suicide. The first convict’s suggestion that they repair the rocket and attempt to return to Earth lifts his spirits. At the end of the play, he notes that the first convict has not changed in the three hundred years that they have been away and that the first convict is again going to prison because of a woman.
The voice from ground control, which announces (in act 3) to the first and second convicts, as their rocket hurtles through space, that their contact with Earth will cease at a distance of five million miles from Earth, which they will reach in three minutes.
The first convict’s wife, who is on the first convict’s mind throughout the play but appears only on the strange planet (act 3), a realm where mental telepathy is possible. The first convict is able to conjure up her image and show her, projected as if on a screen, to the second convict.
The blonde woman, who is assigned to the first convict when he and the second convict return (at the beginning of act 4) from outer space after three hundred years. As a member of the party of the future, she is suited to the second convict, who believes in materials and technological progress and attaches no importance to love. They will likely spend the rest of their lives together.
The brunette woman, who is assigned to the second convict. As a member of the party of the past, she is better suited to the first convict, who falls in love with her. She will likely treasure his memory once they are separated. He is sent in her stead to prison because of politically dangerous ideas stemming from a belief in the value of love.
The security man, who is sent with the robot, both in strange attire, to arrest the first convict and the brunette woman for having subversive thoughts and to give them a choice between “rays,” by which their thoughts will be changed, and isolated confinement in the City of Quiet. They immediately choose the City of Quiet. The first convict grapples with the security man when the latter tries to take the brunette woman away.
The robot, who accompanies the security man on his visit to the first and second convicts and the blonde and brunette women.
The voice from headquarters, which orders that the brunette woman be taken to the City of Quiet alone but then agrees to let the first convict take her place and finish his reports on his trip in space.