This is going to be short. This story was terrible and it has Lovecraft's racism and xenophobia on full display. I think if he could have torched New York and wiped it clean of those he saw as inferior he would have.
The Horror at Red Hook tells a story taking place in the 1920s with a New York police detective named Thomas Malone. Malone is left disturbed by an incident that left several people dead.
Lovecraft then works backwards telling how a rich and eccentric old man named Robert Suydam. Suydam ends up buying property in Red Hook and people are disappearing. The police believe something nefarious is happening, but can't prove it. And then suddenly Suydam seems to be slowly reverse aging and marries a young 20 year old distant relative of his.
The story jumps around too much to really get a handle on the story. Lovecraft doesn't include the Chulthu mythos at all. Instead it seems to be about human sacrifice and Lilith. I don't get what caused Suydam to be turned against unless that was the plan all along. And the ending with Malone being buried after falling into another portal and witnessing what Suydam was up to was pretty lame. The story honestly put me to sleep for a few minutes and I was not happy when I woke up and realized I still want done right this story. It is short though and I finished in it about 25 minutes (nap included).