I really liked this story. It's one of the dozen or so longer stories Lovecraft wrote, coming it at around 11,000 words or so, I believe. Not a huge undertaking, but with my busy schedule it took me about four sittings to get through it.
The story is told in three chapters. It is told through a manuscript left behind by a man named Francis Wayland Thurston, who details how he slowly put together pieces of various stories and news accounts to make a horrible discovery.
In part one we're slowly introduced to the idea that something weird has been going on. Thurston is called upon to rummage through his deceased granduncle's belongings, whereupon he inadvertently unearths evidence that unrelated people all over the world seem to have had similar nightmares on the same specific dates. He also finds a curious little statuette of a winged, crouching, tentacle-faced creature, bearing unrecognized symbols or writing. Notes accompanying it name the figure represented as "Cthulhu."
In part two we delve further into the notes and discover in the piles memoirs of a man named Inspector Legrasse, who made some related and similarly disquieting discoveries of his own. It seems that a swamp cult in Louisiana and a remote tribe halfway across the globe not only seemed to worship this same heretofore unknown (to Legrasse) deity or eldritch being named Cthulhu, but they also performed the same exact rites in the same exact, unknown language.
In part three we learn the story of a sailing ship which encountered opposition during one of its voyages. Presumably, they were attacked by pirates. In reality the opposing ship had been trying to not only same themselves and the other ship, but indeed all of reality by keeping the other ship from proceeding.
No spoilers, but I have to say this is one of my favorite stories yet of this collection. As I say, it's a bit longer but still easily doable. Any HPL fan has no excuse for not having read this one. I'm ashamed it's taken me until I'm 38 to do it.