The U.S. Sea Serpent is submarine-napped by a Winged Man to 29,999 A.D. to fight for the Winged Men against their enemies the Fishmen. Both are mutants of the now extinct human race. The Winged Men have also been busy recruiting from seven other centuries. And although Lt. Kenlon and crew are the most primitive, they possess the most effective weapon...evidently submarines went out of style shortly after this century. Kenlon must resolve the ethical question of aiding one group at the expense of the other. The counter-point views of the other civilizations (one alien) add interest to what is otherwise a frayed-feathered formula.