By means of a remarkable invention Harold Lonsdale comes into communication with Almos, a Martian, and is able to exchange bodies with him, and for a brief time to visit Mars. He finds the planet inhabited by a race far in advance of the men of Earth, living in an ideal community where sin and death have been abolished. In the guise of Almos he meets and loves a Martian, Zarlah. Returning joyfully from the discovery that Almos has decided to remain on Earth forever he is horror-struck to find Zarlah fleeing toward the repellant pole in an arenoid in the hope of being hurled thence to Earth. How the lovers pursue each other among the whirling planets forms the conclusion of the book.