The Old Man and the Sea is the epic story of a deep-sea struggle between an old man and a great marlin. Santiago, the central protagonist, is an unlucky Cuban fisherman, who has not caught a fish in eighty-four days. While some fishermen pity his misfortune, others make fun of the old man’s inability to capture anything worthy of market. For many days, Manolin - his young, devoted apprentice and friend - voyaged off the coast of Cuba with Santiago to fish. But the old man’s lack of production causes the boy’s parents to force him to work for another luckier boat. Although he is no longer fishing with the old man, Manolin continues to bring the old man food, bait, and occasionally the newspaper to keep up with the American baseball games. Despite the boy’s absence and his horrible luck, Santiago still rises early every morning, gathers his harpoon, mast, sail, and bait, and walks down to the shore in order to prepare his skiff for the day’s fishing. He remains confident that he will catch a fish.
On this day, Santiago decides to take his skiff out much farther than usual, leaving behind the island’s shallow coastal waters and venturing far into the Gulf Stream. He hopes that the deep-sea fish will bite his line, whereas the ones closer to the coast had not. He follows the sea birds and flying fish, which he believes would tell him by their movements where the fish congregate. He drops his lines at various depths to attract fish at every level. Early in the day, Santiago lands a 10-pound tuna, which he considers a good sign, and thus he uses some of the fresh meat to bait his lines in the hope that it will attract larger fish. By now, he is far away from land - much farther out than all the other fishermen. Resisting the temptation to sleep or daydream, Santiago concentrates on his lines reaching deep into the dark waters, and around noon, a gigantic marlin takes the bait at 100 fathoms after circling many times. The old man manages to hook the fish in the mouth, but is not able to lodge the hook deep in its stomach where it could kill the fish by tearing into its heart. Instead, the great marlin, only slightly injured, begins to pull the boat out to sea. Santiago ties the reserve line from his other casts to the line with the great marlin. He cannot tie the line to the boat, because the marlin’s great size and strength would break the taut line. Instead, he holds it steadily but loosely in order to allow the fish to swim without struggling free.
The great fish pulls the boat all through the day and into the night, swimming with endurance, strength, and tirelessness to the northwest. Once, when the fish gave a sudden tug, the line slashed Santiago’s cheek. "Fish," the old man says aloud, "I’ll stay with you until I am dead." By morning of the second day, the great marlin still swims robustly, with no signs of tiring. Although there was now no land in sight, the old man was not concerned - he could always find his way home. Home was not the first thing on his mind, however. A treacherous cramp in his left hand and a deep cut in his right hand extremely concerned Santiago, who feared his body might give out on him when he needed to rely on it the most. "I wish I had the boy," he said aloud.
Suddenly, the great fish leaped into the air, as if to show the fisherman what he was up against. The old man marveled at the gigantic marlin, with brilliant lavender scales and a frame two feet longer than the boat itself. It was the biggest and the most beautiful fish the old man had ever seen. The great fish then immediately began towing the boat to the northwest with the same strength it had from the beginning. Santiago could only hold onto the line and wait for the great fish to make its move.
Santiago knew he would need his energy later, and so he ate strips from the tuna he had caught earlier and drank water from his canteen sparingly. While he held the line, his thoughts often drifted to the great fish, the lions, Manolin, or DiMaggio and the Yankees. At one point, Santiago fell into a daydream about an arm-wrestling match he had as a young man. The contest with "the strongest man on the docks" had lasted more than twenty-four hours, but Santiago had endured and won.
Santiago endures constant pain from the fishing line. Whenever the fish lunges, leaps, or makes a dash for freedom, the cord cuts him badly. As he struggles, the old man feels a deep empathy and admiration for the marlin, his brother in both suffering and resolve. On the second night, Santiago allows himself a few moments of sleep. He props the line behind his back against the boat, keeping both hands on the thin cord while he dreams about the lines. The great marlin, however, begins to pull harder than ever, and the feeling of the line running out to sea quickly awakes the old man.
On the third day, the great fish starts to tire and circle the skiff. After hours of struggling, the dizzy, weary, aching old man finally brings the great fish close to the surface. Finally, on one of its many passes by the boat, the old man delivers with all his strength the mortal harpoon thrust into its side and through its heart. "I think the great DiMaggio would be proud of me today," said the old man. He lashes the dead marlin to the skiff, raises the small mast, and sails home to Cuba with the great fish by his side. The marlin’s blood leaves a trail in the water, however, and soon sharks appear to feast on the fresh meat. Swift, hungry Makos and Hammerheads begin tearing hunks of flesh from the marlin’s body. The old man fights them off with any weapon he can find aboard the skiff. First, he drives the harpoon into the sharks’ heads through their brains. But one shark tears the weapon from his hands, and Santiago is then forced to attach his knife to the end of the oar as a makeshift spear. After killing many, the knife breaks, and he is left with only a small wooden club to defend the great marlin. As night falls, the sheer number of sharks and the deep darkness prove too much for the weary old man. The sharks leave only the skeleton, head, and tail behind. Santiago and his bleeding, raw hands were beaten. "I’m sorry, fish," he says to the remains of the great marlin. He arrives at the quiet village harbor before the sun rises, stumbles back to his shack with the mast across his shoulders, and enters a long, deep sleep.
The next morning, a group of amazed fishermen gathers around the skeletal remains of the great fish, which is still lashed to the side of the skiff. Manolin, who feared that the old man was lost at sea, cries when he finds Santiago safe in his bed. When the old man awakes, the boy tells him that the villagers had sent out rescue teams to find him. Santiago tells him the story of the great fish, his suffering, and how he had been beaten in the end by the sharks. Manolin promises to fish with the old man always, regardless of what his parents say. They make plans to buy the equipment that Santiago had lost in the battle, and the boy leaves to get Santiago food, coffee, and medication. While he walks to the local market, Manolin again weeps uncontrollably. The old man falls asleep once more. That afternoon, two tourists observe the carcass of the great marlin and mistake it for a gigantic shark.