The Old Man and the Sea tells the story of Santiago and his epic struggle with a huge marlin. Santiago has been a fisherman his entire life, and he knows that some days, a catch is not to be had. When the story begins, readers learn that Santiago has been having an especially dry patch of fishing. He has not had a catch in eighty-four days, yet he continues to persevere and go out each day with hope that it will be the day that he once again hooks a fish. Santiago's eighty-fifth day is that day.

At around noon, Santiago hooks a large marlin. The fish is incredibly strong, and Santiago fears that he will lose the fish if he ties off the line. Consequently, Santiago's body takes the full force of the fight, and his back, shoulders, and hands are put through unbelievable strains. Santiago battles the fish for the remainder of the day, through the night, through the next day, and through the next night. By the third day, the marlin is tired enough for Santiago to pull it in and kill it with a harpoon. He ties off the fish and begins sailing for home.

Smelling blood in the water, sharks find Santiago and the dead marlin, and they begin to attack Santiago's catch. He valiantly tries to protect his prized fish, but the sharks leave nothing but a skeleton. Santiago arrives home early in the morning on what would be the start of day four.