The old man named Santiago is fishing on his boat in the Gulf Stream. For eighty-four days he goes to the sea and returns without catching a single fish. During the first forty days there is a boy with him - Manolin, his apprentice, but after so many unlucky days the parents of the boy tell him that the old man has bad luck. They send him to another boat the owner of which had a good catch in the first week.
It is hard for the boy to watch the old sailor struggling to feed himself, returning with nothing again and again. The boy goes to the shore every night to help the old sailor carry his fishing gear and prepare some food. The old sailor lives in a hut, covered by palm tree leaves, with some furniture that mostly resembles scrap. He is lonely and poor. Manolin tries to entertain Santiago and cheer him up telling him about American football, the results of latest matches and his favourite player Joe DiMaggio.
Once the old sailor says to the boy that he feels his unlucky streak coming to an end and tomorrow he will sure go far into the sea to catch the big fish. Manolin catches some sardines for his friend to have food and bait for next day. Old man goes to sleep peacefully, dreaming of Africa of his youth.
The next day, early in the morning, Santiago goes fishing. His apprentice helps him to prepare the boat. The old sailor tells him that this day he really believes in his luck. With the other fishing boats Santiago leaves the shore and goes far to the sea he loves so much. Santiago thinks about the sea a lot with tenderness and kindness. He is used to loneliness but he feels connected to the nature around - to birds, to fish, to the sea itself. Even though he catches fish, Santiago still respects it and has gentle attitude towards every living creature over and under the water.
The old man is attentively listening to what is happened it the depth. When one of the lines goes down, Santiago feels that it is a huge and heavy fish that almost drags the boat into the depth. A dramatic duel between human and fish starts and it will last for many hours.
Santiago tries to pull the line but he doesn’t succeed. It is the fish who pulls his boat wherever it goes. The old man regrets that he is alone now, without his apprentice, but he is happy that, at least, the fish drags him aside and not down, to the bottom of the sea.
The duel lasts about four hours and it is almost noon. The sailor thinks that it can’t last long, the fish will soon exhaust itself and Santiago will pull it up. But the fish doesn’t seem to get tired at all and it continues fighting for its life.
The night approaches. The old man is very far from the beach, pulled away by the fish. He sees the fading lights of Havana at the horizon. Santiago is very tired, but still holds the line firmly, throwing it over his shoulder. He constantly thinks of the fish, even feeling sorry for it. The sailor understands that the fish is very old, she is strong and behaves very clever and even strange for a fish. He starts talking to the fish in his mind, saying that he will chase it until one of them die.
Finally the fish is clearly weakened, but so is the old man. He is extremely tired and doesn’t feel his arm holding the line. Finally the line starts to go up and the fish emerges. It glitters in the sun, its head and back of dark purple. The fish has a sword instead of her nose, as long as baseball bat and is two feet longer than the boat. It briefly shows itself and then dives back, pulling the boat into the depth. It is almost a miracle that the old man manages to hold the string at that moment. He doesn’t believe in God, but Santiago recites the prayer, swearing to prove to the fish that a man is capable to endure more than it.
After another day of fight the old man is completely exhausted. Trying to distract himself from his misery he remembers about baseball games. Santiago also remembers how he once competed with Negro, the strongest man in the port, and finally it was Santiago who got the upper hand. He could endure a lot and that was the trait that allowed him to win that time.
The duel continues. The old man holds the line with his right hand, than changes it. The fish briefly comes to the surface and dives again. Santiago prepares a harpoon to finish off the fish when it comes closer but the fish retreats again. The old man, his mind clouded with fatigue, starts talking to the fish, explaining it that it has to die anyway.
Finally, the old man gathers all his strength and will and manages to strike the fish with the harpoon. He is almost unconcious, weak, but he keeps pulling the fish to him. Santiago binds the fish to the boat and start sailing back to the shore thinking that DiMaggio could be proud of him. The old sailor is lucky: the wind blows in the right direction helping him to get home.
After an hour, the first shark, driven by the scent of blood, appears near the boat and bites the sailor’s catch. Santiago hits the shark with a harpoon and the shark sinks to the bottom, dragging with it a harpoon, a rope and a big piece of fish flesh.
After the first one, the whole pack of sharks come, chasing the boat with the great speed. The old man meets them with his knife, entering the melee battle with those who try to attack the fish and killing one of them. Finally the sharks leave the boat alone - they have nothing to eat already.
The sailor entered the bay late at night when everyone was asleep. He tied the sail and stepped out of boat, half-conscious after all these events. Behind the stern of the boat he sees a huge fish tail, but apart from this tail and lower there is only a fish skeleton. The sharks ate everything.
The boy meets the crying old sailor on the beach. He tries to comfort Santiago, reassuring him that from now on they will go fishing together, because he is still an apprentice and needs a master to learn. Manolin believes that he can bring good luck to the old man.
In the morning rich tourists come to Havana and are amazed by the long skeleton with a huge tail. The waiter in the cafe tells them the story of the old man, but it seems they aren’t able to comprehend all the drama that happened last night.