Following a brutal confrontation, the defenders of the stockade find themselves in a dire state. The mutineers, having "had their fill of fighting," have temporarily retreated. However, the cost of the defense is high: Hunter has succumbed to his injuries, and Captain Smollett, though his life is not at risk, has suffered a shot that "nicked his lung," leaving him under strict orders not to move. With the doctor preparing to meet Ben Gunn, the protagonist, described as "only a boy," feels the weight of inaction and chooses to embark on a reckless, solitary mission to locate Ben’s boat.
Guided by the sound of the "squawking laughter" of Silver’s parrot, the narrator tracks the pirates to the shore. Near a white rock, he discovers the object of his search: a boat that is "the simplest, lightest, most basic craft possible." Despite its primitive appearance, suggesting it was "made by men hundreds of years ago," it proves to be a buoyant and functional vessel. This discovery sparks a daring, albeit "foolish," plan: to approach the Hispaniola under the cover of night and cut her loose from her moorings, effectively stranding the pirates and preventing them from taking to the seas.
As darkness and fog descend, the narrator launches his boat, navigating toward the two points of light in the distance: the pirates' campfire on the shore and the Hispaniola anchored in the bay. Upon reaching the ship, he locates the "hawser," the rope securing the vessel. He describes the process of cutting it as a delicate operation, working "fiber by fiber" to avoid the lethal force of the "tight and taut" rope snapping back. As he finishes, he inadvertently eavesdrops on the internal chaos aboard the ship, where pirates like Israel Hands are engaged in a violent, drunken dispute.
With the final strands cut, the Hispaniola begins to drift, catching a breeze and moving away from the shore. The narrator finds himself caught in the wake of the larger ship, narrowly avoiding being "smashed" by its movement. From his vantage point, he witnesses the pirates below deck "wrestling madly," their conflict momentarily interrupted by the sudden realization that their ship is adrift. As the haunting refrain of "Fifteen men on a dead man's chest" drifts across the water from the shore, the narrator realizes his boat has been swept out to sea.
Now at the mercy of the ocean, the narrator cowers at the bottom of his small craft, "shivering with fear" and anticipating an "ocean death" amidst the "immense waves." The narrative concludes on a note of exhaustion and vulnerability; as he drifts further away from the immediate danger of the pirates and the ship, he falls into a fitful sleep, dreaming of his home at the "Admiral Benbow." This transition from an active participant in the sabotage to a helpless castaway highlights the boy’s transformation, as his impulsive bravery leads him into a new, existential struggle for survival far from the terrors of the shore.