At the beginning of the XX century, the collective imagination was fascinated by the discovery of radium (1898-1903). The new metal revealed great ‘virtues’ showing potential and interesting therapeutic applications. Different scientists and scholars, during their popular lectures, also suggested the possible use of the radioactive element for energy production. At the same time, they didn’t hide some risky military consequences, in fact radium could have been exploited to create terrible weapons. In the first decade of the century, the scientific imaginary on radioactivity was supported by performances, public lectures held by eccentric speakers, periodicals and newspapers talking about marvellous, but ambiguous, power of the weird substance. Radium could have been useful against cholera, typhus and tuberculosis but, on the other side, it could have caused considerable burns on the body, as the research of Pierre and Marie Curie had already demonstrated. Public opinion was fascinated and frightened by journals, newspapers, comics and, last but not least, statements of scientists, which used a rich vocabulary based on a long and well-established tradition inspired by religion, spiritualism and magic knowledge. Such expressions as mysterious emanations, invisible messengers, shadows of the fatal fading of the body, magic elements, wonderful care, fountains of youth and gold of the alchemists, were very frequent on Sunday supplements of the main European newspapers. The ambiguous power of radioactive substances exerted a great influence on several science writers and science-fiction novelists. As the likelihood of war fell over Europe in 1914, Herbert G. Wells retreated in Switzerland, where he wrote an antiwar ‘scientific romance’ entitled The World Set Free (written in 1913, and published in 1914). The novel was quite a “jumble of Well’s political ideas” (Zoellner, 2009). It was dedicated to Frederick Soddy and inspired by his popular writing on radium: The Interpretation of Radium (1909). The plot spans thousands of years and revolves around a main topic: an element called Carolinum, a fictional stand-in for uranium. Without any claim of completeness, the paper will explore some significant science-fiction novels published during the first decades of the Twentieth century, trying to establish the relationship with the emergence of a public opinion on radioactivity before the ‘age of the Atomic Bomb’.