After reaching the summit of the fictional Mount Helseggen the Cloudy in Norway, the old man tells the narrator about an event that once occurred on the mountain that unnerved him and weakened his limbs (although the narrator points out that despite the old man's protestations of frailty, he nevertheless lies casually next to a huge cliff that terrifies the narrator). The old man wishes to tell the narrator the story from a good vantage point and asks him to look beyond the clouds into the sea, which the narrator timidly does. The desolate ocean has several craggy islands, and the old man names them before pointing out an unusual change in the water. The narrator hears a roar from the sea, which evinces a furious current that shapes the smaller whirlpools of the water into a huge mile-long funnel. He recognizes it as "the great whirlpool of the Maelström," which the old man terms the Moskoe-ström after the name of the island in the middle.
The narrator offers Jonas Ramus's description of the Maelström while acknowledging that it does not sufficiently describe the power of the vortex. According to Ramus, between the shore and Moskoe, the depth of the water is thirty-six to forty fathoms, but from Moskoe to the distant island of Vurrgh, the water is too deep and the rocks too dangerous for the safe passage of a ship. Whenever a ship comes within a mile of the full force , it is carried to the bottom and slammed against the rocks until the Maelström ceases. The narrator points out that the depth in the center of the Maelström is probably much greater than forty fathoms, and he is unsatisfied by accounts that describe the phenomenon as the result of water colliding in a circular motion in a flood, while being drawn to more fantastic explanations that call the center the entrance to the abyss in the middle of the Earth. The guide, however, disagrees, and the narrator concurs in that the size of the abyss defies understanding.
The old man has the narrator protect himself from the deafening sound of the water and begins to tell the narrator of his own experience with the Maelström in his younger days. In his story, he and his two brothers own a boat and are the only ones brave enough to fish among the islands. The business is lucrative but dangerous, and they are very careful to watch the water, although occasionally they are driven out to sea and only come back through luck. They have always successfully navigated the Maelström but never allow their sons to come on the trip.
One day in July, a terrible hurricane arrives without warning. The man and his brothers had come at the islands around two in the afternoon and begin their return at seven, knowing that the Maelström will be still at eight. The breeze picks up, causing the man to feel worried, and when the breeze leaves, the hurricane arrives, tearing away the masts as well as his younger brother, who has tied himself to a mast for safety. The man and his older brother manage to survive despite being temporarily submerged in the water. Unfortunately, by the time the boat recovers and floats back to the surface, they are caught by the Maelström, and they sense their doom.
The moon lights up the sky so that they can see each other, although they cannot hear each other above the noise, and the elder brother signals to the man, making the latter realize that the watch ran down at seven and that they have missed the time of calmness in the Ström. Now, it is reaching full strength. The ship rides the waves into the air, and he sees that the whirlpool is particularly strong. The waves subside into foam, and the man becomes calm in his despair, thinking of how magnificent it will be to die this way and awaiting his exploration of the Maelström's depths, even if it is at the cost of his life. He is also calmed by the cessation of the wind as they circulate in the pool. His brother tries to let go of his hold on a water-cask and join him in the insanity of his fright, so the man lets his brother have it and takes the cask, at which point the ship lurches and begins to head downward.
The man closes his eyes and waits for his death but eventually opens his eyes and sees that his boat is hanging in the black walls of the Maelström, and the force of the boat's whirling pins him to the boat. He sees a rainbow in the abyss, caused by the movement of the water, and as they slowly spiral downward, the man observes the wreckage that swirls around him. After some time, an idea occurs to him as he observes that small shapes and cylinders seem to descend most slowly into the abyss. He lashes himself to the water cask and cuts himself loose, signaling to his brother to seek nearby barrels. However, his brother refuses to move, so he resigns his brother to his fate and detaches the cask from the boat.
As the man had hoped, the cask sinks much slower than the boat that holds his unlucky brother. By the time it sinks half of the distance between its moment of detachment from the boat and the center of the abyss, the funnel of the Maelström has become calm. The man finds himself on the surface, and during the hour in which the Maelström is still, the waves from the hurricane wash him into the channel, where a boat picks him up. He has been saved, but, as he tells the narrator, his black hair has turned white and his face has rapidly aged, although he does not expect the narrator to believe his tale.
The central character of "A Descent into the Maelström" is an admirable figure who displays intelligence, courage, and calm under pressure. Like the narrator of "The Pit and the Pendulum," he defies his impending death and is the only survivor of the three brothers due to his rational nature and presence of mind. Even before he reveals his story to the narrator, he shows himself to be far more capable than he modestly describes. He calls himself weak and afraid, but he lies down casually next to the edge of a tall cliff, thus impressing both readers and the narrator with his nonchalant bravery. The man's account of his old habit of braving the Maelström in order to fish and of his experience with the Maelström is merely a corroboration of the character he establishes in the opening paragraphs.
Both the narrator and the elder brother serve as foils for the main character, although they contrast with the storyteller in different manners. The narrator is not a timid man, for he climbs to the top of a tall mountain and, with the older man's encouragement, peers over the edge of the crag to observe the view. However, in comparison to his companion, he seems positively weak for having to fight his fear of heights before he can sit up and look into the ocean. On the other hand, the storyteller's older brother mostly matches him in bravery, since they both customarily bet their lives on their timing and ability to cross the Maelström in order to fish, but when death approaches, the brother is neither intelligent nor levelheaded enough to make the same deductions as the protagonist.
The storyteller's ability to overcome emotion and deduce that small cylinders provide the most safety in the Maelström likens him to some extent to C. Auguste Dupin, Poe's exemplar of calm and creative analysis. Despite being an adventure story, the tale nonetheless bears some similarities to Poe's mystery stories in that the story of the Maelström has the aura of a detective's reveal: the storyteller has already successfully resolved the story and is now simply explaining his thinking process to a rapt listener. The narrator of "A Descent into the Maelström" has a role analogous to that of the narrator friend of Dupin, in that he is capable but lacks the final spark that makes Dupin or the old fisherman the hero of their respective stories.
In part because the story shares so much with the detective and admiring sidekick genre, it is organized into a frame story where the outer frame is that of a mountain climb, and the inner frame tells the main story via the form of the reveal. Poe's choice of a frame structure for the story is interesting both because of its advantages and disadvantages. The presence of the outside frame detracts from the effectiveness of the old man's story because his presence indicates that he survived to tell the story, but it provides him with a chance to describe the setting of the Maelström prior to beginning his story so that he does not have to interrupt the path of his narration with extended asides. In addition, the narrator's description of his obviously aged but still relatively able body gives the old man's story the suggestion of authenticity.
"A Descent into the Maelström" takes the theme of the fear of death from "MS. Found in a Bottle" and reverses it. Both stories involve a man who is riding a vehicle on water to his certain death, and in both cases the main character reconciles himself to his fate and decides that if he cannot look forward to continued life, then he can at least look forward to discovering what no man has previously come to know. That being said, whereas the narrator of "MS. Found in a Bottle" overcomes his fear of death by realizing that death can be worth the price of increased knowledge, the main character of "A Descent into the Maelström" realizes that he does not need to take this view and figures out how to save his life so that he never has to enter the abyss at the bottom of the whirlpool.