Hunters Out of Space - Joseph E. Kelleam

Originally published in the May, 1960 issue of Amazing Science Fiction Stories. Jack Odin has returned to the world of Opal, the world inside our own world, only to find it in ruins. Many of his friends are gone, the world is flooded, and the woman he swore to protect has been taken by Grim Hagen to the stars. Jack must save her, but the difficulties are great and his allies are few. (Summary by Elliott Miller)