Henry Kuttner's "We Guard the Black Planet!" (novelette, adventure, free): Some North Europeans are actually aliens!
James Beale, an evil archeologist, along with Captain Morse Damon, has setup an expedition in search of the Black Planet that is supposed to exist beyond the orbit of Pluto. A planet that is not actually black but invisible, covered as it is in an artificial "negasphere"; it doesn't occlude any starfield. On Mars, they'll force the spaceman Nils Esterling to go with them.
The Black Planet is the world of winged people - men & women who fly, the "Valkyries" of the (Norse?) legend. People who once had advanced technology that's now forgotten. A world that once revolved around another sun, but was moved as a ship by its inhabitants to escape a war, & finally parked on the outskirts of Sol.
Here Nils will find his own roots & his lady love. And their tragic end that will leave them wingless & earth bound, after he's forced to kill the two crooks.
Fact sheet.First published: Super Science Stories, November 1942.
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Related: Stories of Henry Kuttner, from 1940s.