Asimov's first full-length science fiction novel in 15 years features an impossible glut of protons, called "Plutonium-186," starter for a two-way energy-flow project between Earth and a parallel universe. Avant Establishment-bucking beings on both sides try to warn of the danger but on the colony Moon scientists draw the logical conclusions. Asimov's following will enjoy the innovative clutter of math, physics, and those oozy para-Universe "Soft Ones," but articulated speculations proceed at a long, slow crawl.