The Old Man and the Sea recounts an epic battle of wills between an old, experienced fisherman and a giant marlin said to be the largest catch of his life. It opens by explaining that the fisherman, who is named Santiago, has gone 84 days without catching any fish at all. He is apparently so unlucky that his young apprentice, Manolin, has been forbidden by his parents to sail with the old man and been ordered to fish with more successful fishermen. Still dedicated to the old man, however, the boy visits Santiago's shack each night, hauling back his fishing gear, feeding him and discussing American baseball — most notably Santiago's idol, Joe DiMaggio. Santiago tells Manolin that on the next day, he will venture far out into the Gulf to fish, confident that his unlucky streak is near its end.

Thus on the eighty-fifth day, Santiago sets out alone, taking his skiffles far onto the Gulf. He sets his lines and, by noon of the first day, a big fish that he is sure is a marlin takes his bait. Unable to pull in the great marlin, Santiago instead finds the fish pulling his skiff. Two days and two nights pass in this manner, during which the old man bears the tension of the line with his body. Though he is wounded by the struggle and in pain, Santiago expresses a compassionate appreciation for his adversary, often referring to him as a brother. He also determines that because of the fish's great dignity, no one will be worthy of eating the marlin.