"The Shadow Over Innsmouth" is a manga adaptation of H.P. Lovecraft's classic horror story, reimagined in a visual format that captures the eerie atmosphere of the original tale. The narrative centers on a young man who travels to the decaying coastal town of Innsmouth, Massachusetts, driven by curiosity about his family's obscure history and the town's dark reputation. Upon arrival, he encounters a community shrouded in secrecy, with inhabitants exhibiting strange, almost inhuman features. The town's eerie ambiance is heightened by its dilapidated buildings, oppressive silence, and the pervasive sense of dread.

As the protagonist delves deeper into Innsmouth's mysteries, he uncovers a horrifying truth: the town's residents have made a pact with ancient, aquatic deities known as the Deep Ones. In exchange for wealth and power, they interbreed with these creatures, resulting in a hybrid lineage that gradually transforms them into monstrous beings. The protagonist learns that his own ancestry is tied to this unholy union, placing him in grave danger as the townspeople seek to ensure his compliance with their dark traditions.

The story builds tension through the protagonist's growing paranoia and the escalating threats he faces. Key characters include Zadok Allen, an elderly drunkard who provides cryptic warnings about the town's history, and the Marsh family, whose patriarch, Obed Marsh, initiated the pact with the Deep Ones. The narrative culminates in a desperate escape attempt as the protagonist confronts the horrifying reality of his lineage and the town's sinister fate. The manga effectively conveys the themes of forbidden knowledge, inherited corruption, and the fragility of human identity, staying true to the unsettling tone of Lovecraft's original work.