The Shadow Over Innsmouth introduces the coastal town of Innsmouth and the amphibious Deep Ones to Lovecraft’s mythos. It’s a well put together story, all about a traveler that decided to take a detour he was warned against and ends up in a town with something of a dark secret.
Overall, the plot is relatively straight forward and even the twist at the end was sort of expected (given the narrators genealogical bent). It’s still interesting to read though and there are some really tense moments and shiver inducing descriptions of the Deep Ones.