The U. S. spaceship Elinor M , while circling Mars to test its gravity, is drawn into the planet's gravitational field when it tries to avoid colliding with a meteor. Astronauts Christopher Draper and Dan McReady, accompanied by Mona, a pet monkey taken along for scientific observation, are forced to abandon their ship in ejector capsules. McReady is killed, but Draper and Mona safely reach Mars' surface. Conditions are rugged, but Draper soon learns to make fire by igniting certain stones that burn like coal, and when his oxygen gives out, he discovers that the stones give off the essential element. The monkey leads Draper to underground caves where he finds drinkable water and edible tubers. A slave escapes from an aircraft belonging to a strange planet and joins Draper on Mars. Draper christens him "Friday" and teaches him English, and the two become fast friends. When Friday's former captors begin to bombard Mars in an attempt to kill the escaped slave, Draper, Friday, and Mona escape through the underground canals of Mars and emerge at the planet's icecap. Just as a volcano erupts, melting the ice and causing a flood, the three are rescued by a U. S. spaceship.