I can't find a good image to associate with this story.
This story focuses on a cop, Detective Malone, who has a fear of large buildings that he attributes to a case he worked on in a district called "Red Hook", which is supposed to be based on New York. He goes on to tell the story, and you follow him back to a case he worked on. Kidnapping was running rampant in Red Hook, as was gang activity, and Malone believed it to be related to what he suspected was an underground cult lead by a man named Robert Suydam. Detective Malone takes you through the case, until finally he ends up in the basement of Suydam's apartment during a raid, and finds a door that opens into this abyss that sounds like it's Lovecraft's idea of hell, in which he witnesses a parade of demonic figures carrying Suydam's corpse. Meanwhile, the apartment is crumbling around him. Authorities later find Detective Malone under the wreckage, laying next to a fetid pool that contains the remains of Robert Suydam, and convince him that the door to hell was all a dream. They also find underground canals leading from Robert's home to different places like the basement of a church and the docks, and are able to confirm that children, etc. have been smuggled through these passageways, which are sealed. Rejoining the Detective in "current day", he goes on to mention that he's heard the passageways have been reopened, etc.
Lovecraft himself apparently didn't like this story, and called it "rather long and rambling", and I have to agree with him. It doesn't have the attention holding brevity of his other stories. There were several times that my mind started drifting. I have noticed, too, in reading about it that it's been panned for racism. I didn't particularly notice it, but again, I couldn't get into this one so I simply may have missed it. However, where this isn't one of my favorites, the storyline itself is one of the more detailed and modern. I believe there've been movies attempted on this and I am not surprised. It's a good storyline. What really stands out to me, though, is the description of this hell that Malone gets sucked into. Lovecraft goes all out in this one, unleashing this powerful torrent of imagery on the reader/listener that demonstrates the depths of this man's twisted imagination. Let me see if I can find a quote to provide to illustrate my point:
"Somewhere dark sticky water was lapping at onyx piers, and once the shivery tinkle of raucous little bells pealed out to greet the insane titter of a naked phosphorescent thing which swam into sight, scrambled ashore, and climbed up to squat leeringly on a carved golden pedestal in the background.
Avenues of limitless night seemed to radiate in every direction, till one might fancy that here lay the root of a contagion destined to sicken and swallow cities, and engulf nations in the foetor of hybrid pestilence. Here cosmic sin had entered, and festered by unhallowed rites had commenced the grinning march of death that was to rot us all to fungous abnormalities too hideous for the grave’s holding. Satan here held his Babylonish court, and in the blood of stainless childhood the leprous limbs of phosphorescent Lilith were laved. Incubi and succubae howled praise to Hecate, and headless moon-calves bleated to the Magna Mater. Goats leaped to the sound of thin accursed flutes, and aegipans chased endlessly after misshapen fauns over rocks twisted like swollen toads. "
Final consensus is that it's probably my least favorite so far, though as aforementioned, some of the descriptive ramblings he goes on when recalling Malone's "dream" are pretty admirable.