The protagonist, Ralph, is a special envoy about to travel to Mars to take part in its colonization. Before departing, he argues with his wife, Joan, who does not want to move to Mars. Upset, he goes to unwind at a spaceport bar, where he happens upon a murder caused by the scarcity of Mars transit passes: a man who failed to get one shoots a passenger who won the right to travel in a public draw. As Ralph subdues the killer, his own Mars pass nearly comes to light, but a mysterious blonde woman warns him. The two leave the bar together. Ralph becomes attracted to her, but ultimately chooses to remain faithful to his wife and parts ways with the woman.
Afterward, Ralph is targeted in two assassination attempts on the road. First, a remotely controlled mechanical snake attacks him, but he manages to kill it. Then, while riding the subway, he is targeted by a female assassin. She accidentally kills a bystander who was talking to Ralph, then escapes. When Ralph gets home, he discovers that his wife has packed her bags and is willing to go to Mars with him.
Before departure, Ralph learns from a senior official at the Colonization Bureau that the Martian colony is being thrown into chaos by a power struggle between two monopolistic giants, Wendell Atomic and Endicott Fuel. The two companies are driving up prices and dragging the public into their feud, bringing the colony to the brink of collapse. Ralph's mission is to go to Mars and resolve the crisis.
Aboard the spacecraft to Mars, Ralph encounters the mysterious blonde woman who warned him at the bar. She is a spy planted by the Wendell Corporation. She had intended to assassinate Ralph but had never found the chance. One day, she enters the ship's chart room without permission, and a confrontation breaks out when the crew discovers her. Ralph intervenes to save her. In the scuffle, they accidentally activate one of the ship's robots. It runs amok and crushes a crew member to death.
