Samples of plutonium-186 begin appearing in a scientific laboratory in place of tungsten. Plutonium-186 can exist only in a universe in which the nuclear reaction is much weaker. The element is a source of energy in the human universe, as is the tungsten in the alien universe.

The novel consists of three novellas. The first, Against Stupidity, is a story of professional jealousy and scientific persistence in getting plutonium-186 accepted and used. The second novella, The Gods Themselves, takes place in the alien universe, where mating consists of the merging of three different nebulous creatures. One of them is uneasy about the transfer of material and the prospective mating and sends warnings to the human universe. This is the most engrossing of the three. The third novella, Contend in Vain, describes life on the moon and the effort to stop catastrophe to the human universe by constructing “cosmeg pumps” on the moon and using part of the energy to counteract the changes in field intensity that threaten to explode the sun and perhaps even the galactic arm.