A Colour out of Space
West of Arkham the hills rise wild…
A Colour out of Space is one of my favorite Cthulhu Mythos stories. I reread it recently to coincide with the H.P. Podcraft Literary Podcast episode on the story. As Lovecraft's stories are now out of copyright, you can read this online and at only 12000 words (about 18 A4 pages) it can be read quickly too. You may find Kenneth Hite's Tour de Lovecraft entry for this story interesting.
The guts of the story revolves around a farming family in the Arkham hinterland and their contact with an other worldly being. It is an anticlimactic horror tale backed by early science fiction retold by an unnamed narrator. Lovecraft's themes of rational fear and an uncaring universe are present and powerful, but the lurid and tangle prose of his earlier writing is thankfully absent.