When Lessing published "Shikasta" in 1979, the first book in her "Canopus in Argos" series, it represented a major shift of focus for the author. In her earlier books, Lessing had established a name for herself as a writer of realistic fiction; in "Shikasta" she introduced her readers to the spiritual and mystical themes in Sufism. In the mid-1960s Lessing had become interested in Sufism, an Islamic belief system, after reading "The Sufis" by Idries Shah. She described "The Sufis" as "the most surprising book had read", stating that it "changed [her life". Lessing later met Shah, who became "a good friend teacher". In the early 1970s Lessing began writing inner space fiction, which included the novels "Briefing for a Descent into Hell" (1971) and "Memoirs of a Survivor" (1974), and in the late 1970s she turned to science fiction when she wrote "Shikasta", in which she used many Sufi concepts.