The story hangs its hat on a clever observation made long ago by many physicists, including Einstein, about the nature of solutions of Maxwell's equations. Since the equations are time-symmetric, they entertain both causal (past to future, "retarded" waves) and anti-causal (future to past, "advanced" waves which originate in the future and propagate to the past in just the right manner to converge on a charged source) solutions. At one point, it was thought that a combination of these solutions could explain the stability of Bohr's atom, before Quantum Mechanics came to fore, with the associated price that you had to allow effects preceding cause in at least some limited domain of Physics. The natural question was: if we see light as a manifestation of the retarded solution, why don't we see some kind of "anti-light" from the future as well? [see Feynman-Wheeler’s absorber theory]
Pierce has used this "light from the future" idea as a central theme of a very weak story. A mathematician (world's best, naturally. "He’s the man, who at the age of 20, found the Stuart-Binnet solution to the unified field equations....") picks up on the "Lorentz,-Maxwell-"Mahler" equation (Mahler fictitious) and predicts that the "advanced potentials" solution will be found to have an independent physical reality. He goes on to build a time-viewer which can look into the future (about 10 mins or less; the author makes heavy weather of it and does not really specify this), love with his employer's daughter follows, an accident is averted and all ends pulpy well.
This really could have been quite a strong story if the author had spent some time building a proper plot and explained the principles.