The novel first took shape in July 1946, when Clarke wrote "Guardian Angel", a short story that would eventually become Part I of "Childhood's End". Clarke's portrayal of the Overlords as devils was influenced by John W. Campbell's depiction of the devilish Teff-Hellani species in "The Mightiest Machine", first serialized in "Astounding Stories" in 1934. After finishing "Guardian Angel", Clarke enrolled at King's College London and served as the chairman of the British Interplanetary Society from 1946 to 1947, and later from 1951 to 1953. He earned a first-class degree in mathematics and physics from King's in 1948, after which he worked as an assistant editor for "Science Abstracts". "Guardian Angel" was submitted for publication but was rejected by several editors, including Campbell. At the request of Clarke's agent and unbeknown to Clarke, the story was edited by James Blish, who rewrote the ending. Blish's version of the story was accepted for publication in April 1950 by "Famous Fantastic Mysteries" magazine. Clarke's original version of "Guardian Angel" was later published in the Winter 1950 issue of "New Worlds" magazine.