When the power of the sun becomes noticeably diminished, young Burl Denning and his expedition take off in an anti-gravitational ship to discover the cause and its location. After a dizzying tour of all the planets, they realize that the trouble springs from Pluto, a belligerent planet which is trying to usurp the life-giving power which the sun gives earth. Making an alliance with the friendly Neptunians, the earth expedition represses the Plutonian plot and all ends well for the good folks of U.S.A. An ambitious fantasy based on scientific theory by the author of The Secret of the Martian Moons and The Secret of Saturn's Rings. For science fiction devotees.