Lovecraft matures.

As Lovecraft continues writing short stories, he also noticeably becomes a more solid writer. He now has a more comprehensive vision of a parallel universe filled with horror, the Cthulhu Mythos that made him famous. In this respect, Lovecraft is also a more modern writer. He goes a step beyond Poe himself and becomes what we could call the J.R.R. Tolkien of the horror genre (i.e., a writer who doesn't only write stories but who manages to create a whole universe, a separate world, a parallel reality with its own set of rules and traditions). Among the stories included in this volume, one can clearly perceive a gradual evolution towards a more settled down, more solid narrative in The Colour Out of Space (1927) and The Whisperer in Darkness (1930) but it's with The Shadow Over Innsmouth (1931) that we can already tell the author reached a new plateau. The nearly 15 pages where the main character explains how he managed to escape from the strange creatures in Innsmouth is a masterpiece of the genre for, in spite of the length of the description, Lovecraft never lets us go. The story becomes a page turning frenzy at that point. The end of the story is no less of an achievement, although obviously set at a completely different pace when the narrator realizes that he is quickly becoming one of the beasts he despised so much.

My great-grandmother had been a Marsh of unknown source whose husband lived in Arkham —and did not Zadok say that the daughter of Obed Marsh by a monstrous mother was married to an Arkham man through a trick? What was it the ancient toper had muttered about the likeness of my eyes to Captain Obed's? In Arkham, too, the curator had told me I had the true Marsh eyes. Was Obed Marsh my own great-great-grandfather? Who —or what— then, was my great-great-grandmother? But perhaps this was all madness.

(...)

For more than two years I fought off these reflections with partial success. My father secured me a place in an insurance office, and I buried myself in routine as deeply as possible. In the winter of 1930-31, however, the dreams began. (...) Some frightful influence, I felt, was seeking gradually to drag me out of the sane world of wholesome life into unnamable abysses of blackness and alienage; and the process told heavily on me. (...) It was then that I began to study the mirror with mounting alarm. (...) What was taking place in me? Could it be that I was coming to resemble my grandmother and uncle Douglas?

(Lovecraft: pp. 333-334)

The story ends with a true cliff-hanger. It's not, nevertheless, the sort of cheap cliff-hanger one sees in today's movies though. Lovecraft leaves the story wide open, clearly suggesting that the horrible creatures associated to the dark events in Innsmouth (i.e., the creatures he is quickly joining) may rise some day and destroy our world:

The Deep Ones could never be destroyed, even though the palaeogean magic of the forgotten Old Ones might sometimes check them. For the present they would rest; but some day, if they remembered, they would rise again for the tribute Great Cthulhu craved. It would be a city greater than Innsmouth next time.

(Lovecraft: p. 334)