One legendary insect - enormous, white, and exceedingly rare - attracts trout of such size that they couldn't possibly exist in the world as we know it. But in Heywood's classic novel, such things can and do exist.
Protagonist Bowie Rhodes, a UPI reporter and expert fly fisherman, learned of the snowfly as a child. It hatches every seven to ten years, never on the same river twice, bringing to rise unimaginably huge trout, so wily that they never allow themselves to be caught - or even seen; trout so hungry for this fly that they will risk exposure to rise for the hatch. The snowfly is the sacred quest of the most obsessed trout hunters, existing - it seems - only in myth and in a lost manuscript.
Rhode's reporting bring him to such sites as the jungles of Vietnam, the labyrinth of Brezhnev's Soviet Union, and a poisoned Canadian wasteland of uranium mines. His hunt for the manuscript also takes him deep into his own psyche.