The story has its origins in Price's enthusiasm for an earlier Lovecraft tale. "One of my favorite HPL stories was, and still is, 'The Silver Key'," Price wrote in a 1944 memoir. "In telling him of the pleasure I had had in rereading it, I suggested a sequel to account for Randolph Carter's doings after his disappearance." After convincing an apparently reluctant Lovecraft to agree to collaborate on such a sequel, Price wrote a 6,000-word draft in August 1932; in April 1933, Lovecraft produced a 14,000-word version that left unchanged, by Price's estimate, "fewer than fifty of my original words," though "An H. P. Lovecraft Encyclopedia" reports that Lovecraft "kept as many of Price's conceptions as possible, as well as some of his language." Thus many of the central ideas of the story like 'Umr at-Tawil, the talk of mathematical planes and multiple facets of Randolph Carter throughout Time and Space come from Price, who was well read in neoplatonic thought, theosophy and the occult. Even the quote from the Necronomicon is mainly by Price in outline though put in more Lovecraftian language. The sub-plot about Yaddith was entirely Lovecraft's idea however. Hoffman Price's tales were oriental, and 'Umr at-Tawil was merely an Arab who had preternaturally long life in his draft.