The narrator begins by describing the town of Bloomsville, Mississippi, which appears unremarkable unless the Mississippi River overflows. He compares a seemingly trivial event in Bloomsville to the ripples caused by a pebble thrown into a pond, suggesting that significant events can arise from small beginnings, influenced by faraway actions.

The story unfolds as the narrator and his friend, "Hawk" Egan, sit on a log by the riverbank. They watch a large passenger steamer pass by when suddenly, a man dives overboard into the water. The narrator is alarmed, but Hawk, known for his sharp vision, asserts that the man did not fall but deliberately dived. Hawk further identifies the man as neither white nor black but having a mustache atypical for either race. He speculates that the man swam underwater to the shore.

After a brief argument, the two friends part ways. The narrator returns home, where his sister Marion persuades him to accompany her on a flower-picking outing, despite his reluctance. They travel inland, and while Marion gathers flowers, the narrator dozes off. He awakens to find a mysterious man, matching Hawk's description, standing over him with a small bundle and a hand inside his coat, possibly holding a weapon. The man, appearing frightened, quickly disappears into the underbrush.

Curious, the narrator follows the man stealthily, observing him hide the bundle in a hollow tree before fleeing. The narrator retrieves the bundle, which contains a large, richly bound book with strange symbols on the cover. Realizing the potential danger, he also flees the scene.