Santiago is an elderly fisherman who has not caught a fish in eighty-four days and is considered salao (very unlucky). Manolin, who had been trained by Santiago, has been forced by his parents to work on a different, luckier boat; Manolin still helps Santiago prepare his gear every morning and evening and brings him food. They talk about baseball and Joe DiMaggio, before the boy leaves and Santiago sleeps. He dreams of the sights and experiences of his youth.
On the eighty-fifth day of his streak, Santiago takes his skiff out early, intending to row far into the Gulf Stream. He catches nothing except a small albacore in the morning before hooking a huge marlin. The fish is too heavy to haul in and begins to tow the skiff further out to sea. Santiago holds on through the night, eating the albacore after sunrise. He sees the marlin for the first time—it is longer than the boat. Santiago increasingly appreciates the fish, showing respect and compassion towards his adversary. Sunset arrives for a second time and the fisherman manages some sleep; he is awoken by the fish panicking but manages to recover his equilibrium. On the third morning the marlin begins to circle. Almost delirious, Santiago draws the marlin in and harpoons it. He lashes the fish to his boat.
A mako shark smells blood in the water and takes a forty-pound bite of the marlin. Killing the shark but losing his harpoon, Santiago lashes his knife to an oar as a makeshift spear and kills three more sharks before the knife blade snaps. Cursing himself for going out too far, he apologises to the mutilated carcass of the marlin. He clubs two more sharks at sunset, but the marlin is now half-eaten. In the third night, the sharks come as a pack and leave only bones behind them. Santiago reaches shore and sleeps in his shack, leaving the skeleton tied to his skiff.
In the morning Manolin cries when he sees Santiago's state. He brings coffee and sits with Santiago until he wakes. He insists on accompanying Santiago in the future. A fisherman measures the marlin at eighteen feet long, and a pair of tourists mistake its skeleton for that of a shark. Santiago goes back to sleep and dreams of lions on an African beach.
