Russell's Sinister Barrier, the novel that had persuaded Campbell to set his plans for a fantasy magazine into motion: the plot, involving aliens who own the human race, has been described by SF historian Mike Ashley as "a strange mixture of science fiction and occult fantasy". Campbell asked Russell for revisions to the story to emphasize the fantastic elements but still demanded that Russell work out the logical implications of his premises. This became a defining characteristic of the fiction published in Unknown; in Ashley's words, Campbell "brought the science fiction rationale to fantasy". The first issue also contained Horace L. Gold's "Trouble with Water", a comic fantasy about a modern New Yorker who offends a water gnome; in its whimsicality and naturalistic merging of a modern background with a classic fantasy trope, "Trouble with Water" was a better indication than Sinister Barrier of the direction Unknown would take. Campbell commented in a letter at the time that Sinister Barrier, "Trouble with Water", and Where Angels Fear ... by Manly Wade Wellman were the only stories in the first issue that accurately reflected his goals for the magazine. Under Campbell's editorial supervision, the fantasy element in Unknown stories had to be treated rigorously. This naturally led to the appearance in Unknown of writers already comfortable with similar rigor in science fiction stories, and Campbell soon established a small group of writers as regular contributors, many of whom were also appearing in the pages of Astounding. L. Ron Hubbard, Theodore Sturgeon, and L. Sprague de Camp were among the most prolific. Hubbard contributed eight lead novels including Typewriter in the Sky, Slaves of Sleep, and Fear, described by Ashley as a "classic psychological thriller"; SF historian and critic Thomas Clareson describes all eight as "outstanding". De Camp, in collaboration with Fletcher Pratt, contributed three stories featuring Harold Shea, who finds himself in a world where magic operates by rigorous rules. The title of one of these, "The Mathematics of Magic", is, according to SF critic John Clute, "perfectly expressive of the terms under which magic found easy mention in Unknown". Other Astounding writers who wrote for Unknown included Robert A. Heinlein, whose "The Devil Makes the Law" (reprinted as "Magic, Inc.") depicts a world where magic is a part of everyday life. Heinlein also contributed "The Unpleasant Profession of Jonathan Hoag" and "They", described by Ashley as "perhaps the ultimate solipsist