An adventurer from Earth named Kilgour travels to Venus and becomes the first man to set foot on the planet. He discovers a miraculous-seeming can of paint, evidence of intelligent life on Venus, which he accidentally spills on himself. The paint does not follow any known laws of the universe. Kilgour becomes worried that he will die, suffocated by the paint which he cannot get off and which continues to spread to cover more of his body. To his surprise, Venusians respond to his distress calls and tell him that it is a test to determine if humans are fit to visit Venus. If he solves the puzzle and gets the paint off before he dies, they will allow humans of his intelligence level and higher to interact with their society, which is clearly more advanced than Earth. In the knick of time, Kilgour solves the riddle by noticing that the paint reacts to light and energy and is therefore diminished by complete darkness. He leaves Venus with an exclusive contract and a cargo-full of the wonder-paint to sell back on Earth.