"All dead. Edith, Stanton, Thora -- dead -- or worse. And Edith in the Moon Pool -- with them -- drawn by what you saw on the moon path -- that has put its brand upon me -- and follows me!"

As Dr. David Throckmartin gasps out the horrible climax to the story of his expedition among the ruins of an ancient Pacific civilization, Dr. Walter Goodwin listens to his incredible tale, certain that the great scientist has gone mad. For he has told of how his young bride Edith and other members of his exploring party were spirited away by the unearthly, androgynous Dweller of the Moon Pool -- a "thing"" that arises at the full moon from the wailed ruins of an ancient Polynesian culture and manifests itself amid the fainting chanting of voices, a drifting, undulating, crystalline chiming, and a glittering cluster of palely colored lights. Its embrace induces feelings of both rapture and terror in its prey, a state that Throckmartin describes was "as though the icy soul of evil and the fiery soul of good had stepped together within me."

Bearing the peculiar small white mark of the Shining One, Throckmartin had miraculously escaped the fate of his friends. And then, before Goodwin's eyes, aboard the ship that is bearing them both across the Southern seas beneath another full moon, Throcmartin disappears in the glistening embrace of the pursuing Dweller of the Moon Pool.

Determined to solve the mystery of the Moon Pool and learn the fate of Throckmartin and his party, Goodwin sets out on an expedition that includes among its members an Irish air ace, a huge modern Viking and a sinister Soviet scientist. Following Throckmartin's directions to the island ruins, the party plunges into a fantastic adventure off the site of the Moon Pool that is an imaginative tour de force seldom equalled in science fiction.