Set in the eighteenth century, Treasure Island is narrated by the teenage boy Jim Hawkins, whose father owns the Admiral Benbow inn. An old seaman named Billy Bones, who identifies himself as “The Captain,” takes up lodging at the inn and promises Jim a monthly allowance if he keeps an eye out for a “seafaring man with one leg.” After several months, the captain receives two unwelcome visitors. The first one, a pale man called Black Dog, converses with the captain in private before the latter chases him out of the inn with his cutlass. The effort, however, causes him to suffer a stroke and collapse. The second visitor, a blind beggar named Pew, comes while the captain is bedridden and presses a note onto his palm. After Pew leaves, the captain suffers another stroke and drops dead.

Since the captain’s death came soon after that of Jim’s father, Jim and his mother are left in a precarious predicament. After searching the captain’s corpse for his key, they open his sea chest and take what is owed them—as well as a mysterious oilskin packet, which contained a treasure map originally belonging to the notorious pirate Captain Flint. Soon after the two flee the Admiral Benbow, a crew of buccaneers, Pew and Black Dog among them, arrive and tear apart the inn in search of the map. The buccaneers are then dispersed by a group of officers on horseback and, in the scuffle, Pew falls down a ditch and dies. 

The same night, Jim rides to the local physician and magistrate, Dr. Livesey, and finds him with squire John Trelawney. Upon inspecting Flint’s map, the two men decide to sail for the treasure and bring Jim along as the ship’s cabin boy.

After a few weeks, Trelawney successfully procures a schooner, named the Hispaniola, and a crew that included Long John Silver, a sea cook with only one leg. While initially suspicious of Silver, Jim is eventually won over by the cook’s kindness and easy charm. The Hispaniola sails under the command of Captain Alexander Smollett, and their voyage proves to be smooth apart from the inexplicable disappearance of Arrow, the first mate.

One night, after having fallen asleep inside an empty apple barrel, Jim overhears Silver and several crewmen reminiscing about their time as part of Captain Flint’s original band of pirates. He also learns of their nefarious plot to take Flint’s treasure for themselves and murder the rest of the ship’s men in the process. Before landfall the following day, Jim informs his three foremost allies—Dr. Livesey, Trelawney, and Captain Smollet—of Silver’s plan.

Upon reaching their destination, Skeleton Island, Captain Smollet gives the crew permission to explore the land as they please—Silver, along with some of his men, takes up this offer. Meanwhile, Jim runs off to chart the island on his own. There, he witnesses Silver murder Tom, one of the crewmen, after the latter refuses to take part in their scheme. While fleeing the scene, he stumbles onto the shaggy figure of Ben Gunn, a former crewman of Captain Flint’s who was marooned on the island three years ago. The two become allies.

In Jim’s absence, Dr. Livesey, having found the stockade indicated on Flint’s map, decides to abandon the schooner with Captain Smollett, Trelawney, and the few loyal men they have left. The mutineers fire at them as they leave and one of Trelawney’s men, Redruth, is shot dead. In the relative safety of the stockade, Captain Smollett climbs to the roof and hoists the British colors. Shortly thereafter, Jim joins their company and tells them of his encounter with Ben Gunn.

The following morning, Silver approaches the stockade with a flag of truce. Once received, he tries to bargain with Captain Smollett for Flint’s map, promising them safe passage on the Hispaniola—and even a portion of the treasure. After Smollett turns Silver away, the stockade is assailed by the mutineers. Five of the pirates and one of Trelawney’s men perish in the fray, while Captain Smollett sustains grievous injuries.

That evening, Dr. Livesey departs from the stockade to find Ben Gunn, while Jim decides to sneak out to the Hispaniola. He finds the crude makeshift boat Ben Gunn told him about and maneuvers it to the schooner. After cutting the rope which secured the Hispaniola to the shore, Jim falls asleep inside the boat. The next morning, he boards the schooner after judging it to be unmanned. On the deck, he finds the aftermath of a violent drunken quarrel between two of the mutineers: one lies dead while the other, Israel Hands, is gravely wounded.

In exchange for rum, Hands instructs Jim on how to sail the Hispaniola. After Jim successfully lays the schooner near the northeast part of the island, however, Hands attacks him. He is forced to shoot the pirate dead. It is well after dusk when Jim arrives back at the stockade—where he is shocked to find Silver and his men. Silver informs Jim that Dr. Livesey surrendered the stockade when they noticed that the Hispaniola was gone. He propositions Jim into joining them, but the latter vehemently declines, revealing that it is he who has continually foiled the sea cook’s schemes. The mutineers wish to murder Jim and depose Silver as captain, but the latter is able to appease their tempers. In private, Silver and Jim agree to protect each other.

The next day, Dr. Livesey visits the stockade to treat the wounded mutineers. He privately implores Jim to escape with him; out of respect for Silver, Jim refuses. However, he informs Dr. Livesey of the secure state of the Hispaniola—much to the doctor’s great relief.

During the treasure hunt, the pirates stumble upon the chilling skeleton of one of Flint’s old crewmen. Their fright is compounded by a disembodied voice singing Flint’s well-known sea shanty. However, the pirates soon figure the voice to be Ben Gunn’s, and their greed drives them to continue in their pursuit.

Upon reaching the location of the treasure, the men are furious to find the chests already excavated and emptied. Blaming their misfortune on Silver, the pirates move to attack when muskets are fired from behind—killing half of the men, with the remaining survivors fleeing. Dr. Livesey, Ben Gunn, and another one of their allies reveal themselves to be hiding among the trees.

It is revealed that Ben Gunn had long ago found and collected the treasure during his exile. The following day, Jim and his allies load Flint’s treasure on the Hispaniola and leave the island, as well as the surviving mutineers. While casting anchor at the nearest port, Silver pilfers a sack of coins and escapes—much to the relief of the company. The rest of the men return home and divide the riches equally among them. Jim ends his account by confessing that he is still plagued by nightmares of Skeleton Island.