He seeks forbidden aid from the Worms of the Earth, a race of creatures who Bran Mak Morn's ancestors banished from their kingdom centuries ago.
The witch's price for helping him is "one night of love" which her human half craves — as men in general are repelled by her reptilian traits.
In a 1932 letter to August Derleth, Clark Ashton Smith, discussing the current issue of Weird Tales, stated that "Howard’s 'Worms of the Earth' seems to be the one real first-rater.
Twice in Worms of the Earth Howard mentions the "black gods" of R'lyeh, a fictional city created by his friend and correspondent H. P. Lovecraft.
Howard had previously dealt with beings similar to the titular Worms of the Earth in an earlier short story, "The Children of the Night", set in Lovecraft's Cthulhu Mythos.