As Lord Glenarvan and his wife, Lady Helena, are cruising in their yacht, "Duncan," off the coast of their native land, Scotland, the crew harpoons an immense whale which discloses when it is disemboweled a bottle with a message referring to Captain Grant, who had set out in quest of land to colonize and who had lost his ship, the "Britannia," in latitude 37 degrees off the coast of South America. The interpretation of the message is rather uncertain, as the writing had been nearly obliterated. An advertisement in a daily newspaper to the effect that data concerning Captain Grant has been found brings Robert and Mary Grant, children of the shipwrecked mariner, to the residence of the lord to entreat him and his wife to sail for Patagonia to see if their father cannot be found. Lord Glenarvan assents, and, when on the ocean a few days, a stranger, who had mistaken the "Duncan" for the good ship "Scotia," upon which he was to sail to India, makes himself the laughing stock of the crew by speaking of the "Scotia," of its captain and of India. The stranger is recognized by the lord and his wife as Panganel, a learned geographer. He consents to accompany the expedition, and forty-two days later the yacht arrives at Concepcion, in Chile. The party are unable to obtain any data from the British consul concerning the shipwrecked captain, and they are in despair. Their sorrow is allayed, however, by Panganel who, after trying to make a more correct translation of the message, says that Grant must have been taken prisoner in the interior of South America. While Lord Glenarvan starts to cross the continent, following the 37th parallel as the document indicates, Tom Austin, the mate of the "Duncan." will double Cape Horn and await the party in the Atlantic at the 37th parallel. Abandoned by the guides at the foot of the Alps due to their fear of recent earthquakes, the party is led by Panganel. Toward night they take refuge in a hut which stands upon a glacier which later starts moving down the precipitous mountainside. They all escape with their lives, but discover that Robert is missing. Suddenly a condor soars through the air and they perceive Robert in its talons. They do not shoot for fear of killing him, but a peasant, with unerring aim, brings the bird to the ground and thus saves Robert's life. The peasant is found to be a Patagonian chief and he offers to guide the party through the vast wastes of land. Thalcave, the Patagonian chief, assists them in purchasing horses and supplies. The water supply gives out as they are crossing the desert, and Thalcave, who knows where water can be obtained, leaves the party in company with the lord and Robert. They come to the stream, but find that it is impossible for them to get back to the camp before night comes on, so they repair to an abandoned hut, where they are not long afterward disturbed by a herd of wild cattle. Robert essays to go for help. Mounted on his fleet-footed horse he out-distances the mad cattle, which are in pursuit of him, and reaches the camp safely. Thalcave and the lord arrive a short while later with the water. Heavy rains follow the drought and the surrounding country becomes a veritable lake. The adventurers seek safety in a tree, which is uprooted by the hurricane that comes on with nightfall. The party still clings to the immense tree and are thankful when the wind, which has subsided considerably, blows it upon a hill. From the top of the hill they perceive the "Duncan" and it is not long before they are on board. The party has crossed South America, but no trace of Captain Grant has been found. The message is again interpreted and it is found that a mistake had been made; the party should have gone to Australia instead of to South America. Arriving in Australia, the lord is accosted by a person named Ayrton, who offers his services as guide. He shows the lord a paper which states that he was once the quartermaster on Captain Grant's ship, but had left before the shipwreck. As a matter of fact he was discharged for inciting mutiny. As Ayrton, he is known as a peaceful miller; as Ben Joyce, he is the leader of a band of pirates. The lord, unconscious of his true character, hires Ayrton, and the party sets out for Melbourne, the men on horseback, the women in wagons drawn by oxen, while the "Duncan" is to sail to Melbourne under the command of Tom Austin. When an opportunity presents itself, Ayrton begins to put into effect his malignant scheme and starts in by poisoning the horses and oxen. The lord escapes on horseback to the nearest railway station to go to Melbourne to bring the crew of the "Duncan" to the assistance of the party. Ayrton, fearing discovery, secretly leaves the camp, but is shadowed by Robert to the rendezvous of the convict band. There he learns that they are to wreck the train in which the lord will he traveling. He rushes back to the camp, takes a swift steed, and dashes after the train. He catches up with it, climbs from the saddle of his horse on to the platform of the train, uncouples the car in which the lord is riding from the rest of the train and saves the lord's life. The lord and his young rescuer go back to camp only to come face to face with Ayrton, who thought that he had killed the lord. There is a struggle, in which the lord is wounded. Ayrton escapes. The "Duncan" must be reached and the lord, unable to use his right arm, dictates a letter to Tom Austin instructing him to sail to the 37th parallel on the east coast of Australia, from where he is to send a relief column to succor the party. But Ayrton has been eavesdropping and has heard the contents of the letter, so when the messenger, Mulready, who is to deliver the letter is on his way, he is intercepted by the pirate and seriously wounded. The party sets out a little later than the messenger, and they come upon him just in time to hear his dying words: "Stolen, the letter, Ayrton." After several days of hard and tedious traveling the party reaches the east coast of Australia, but no trace of the "Duncan" can be found. The lord charters a ship to reach Melbourne, but as she is in the hands of a drunken crew she founders off the coast of New Zealand. The adventurers escape by swimming, but upon coming ashore are made prisoners by the Maoris. The lord kills one of the tribe and in the melee that follows Panganel and Robert manage to escape. The prisoners' day of doom arrives on the morrow, and as they are cheering one another so that they may take their fate calmly, Robert and Panganel effect their rescue. They seek shelter in the Temple of Tabou, but are pursued by the Maoris. The captives blow up the sanctuary and escape by a subterranean passage to the sea. In the distance they observe a ship and embarking in canoes make for it, with the natives in hot pursuit. Death seems to threaten the lord and his associates by land and by sea. As he approaches the "Duncan," it would seem as if the ship were in the hands of pirates, for they open fire. But they aim at the pursuing Maoris, who are annihilated. Ayrton is a prisoner aboard the yacht. No trace of Captain Grant can be found and there is nothing for Lord Glenarvan to do but to return to Scotland. In the evening as the yacht is lying at anchor, Robert, who is walking the decks with his sister, sees in the offing a light. A cry of "Help," is then heard. Robert tells the man at the helm, but he ascribes it to the imagination of the youth. Morning breaks with the children disconsolate. A rocky promontory heaves in sight through the morning mist. Boats are lowered and directed toward the shore. Suddenly there bursts from the lips of Robert and Mary a cry of triumph. Upon a rocky headland stands a pathetic figure stretching out his arms to the children. It is their father. Their hearts are ready to burst with joy. Ayrton is marooned on the desert isle. As the "Duncan" sails homeward, the bandit can be seen silhouetted against the sky. The foiled desperado cannot deny a parting salute to the victims of his baseness, and the cannons of the yacht vomit forth a parting salute in reply, and that is the last of Ayrton.