"Sign of the Labrys" (1963), set in a vast underground shelter after the world has been depopulated by plagues, featured an overt early use of Wicca elements in fiction; St. Clair wrote that the book "was primarily inspired by Gerald Gardner's books on witchcraft." The editor of "The Crystal Well" called "Sign of the Labrys" "an occult classic," and in his review of the novel for "Analog", P. Schuyler Miller declared that St. Clair was one of the most unappreciated writers in science fiction. St. Clair's research into witchcraft led to her friendship with Raymond Buckland, who recalled the St. Clairs as "absolutely wonderful people, very warm and loving."