A man is seen walking along hilly terrain near the sea. When he walks nearer to the camera and we see his face in closeup, we hear the words "Call me Ishmael," He is the narrator (Richard Basehart), a young man who has experience in the merchant marine but has recently decided to see a different world by signing on to a whaling ship. By nightfall he arrives at the Spouter Inn in New Bedford, Massachusetts, and agrees to share a bed with a then absent stranger. He enjoys drinks at the inn and as he waits for night he is told of the rules for seeking work on whaling ships by Stubb (Harry Andrews). He is questioned, and after his answers are deemed satisfactory he is accepted by a group of seamen and he joins in drinking songs with them. During the storm, they spot the mysterious Captain Ahab (Gregory Peck) walking in the rain
When his room and bed mate, a heavily tattooed Polynesian harpooner named Queequeg (Friedrich von Ledebur), returns very late and discovers Ishmael in the bed under the blankets, both men are alarmed, but the two quickly become close friends and decide to sail together on a whaling ship.
The duo signs on with the Pequod, a whaling ship that is soon to leave port. Two owner partners make the hiring decisions and negotiate the compensation, which is a fraction of the profit from the voyage. They are suspicious of Queequeg but he shows his marksmanship with the harpoon and they gladly accept him at 1/300 fraction, where Ishmael only gets 1/600. The ships captain, Ahab, is nowhere to be seen; nevertheless, the owners speak of his solid reputation and legendary experience.
On a church near the ships, townspeople and seamen gather for a Sunday service. The pastor, Father Mapple (Orson Welles) gives a sermon based on the story of Jonah and how after his earnest prayer he was saved from the great whale.
The two pals encounter a man on the dock as they walk to board the Pequod, a man seeming either crazed or drunk (Royal Dano), and he makes a prophecy, that the day you smell land where there is no land, that day Ahab will meet his death, and after he will return and beckon others save one to follow him. When asked his name, he answers "Elijah".
The ships second rank officers direct the first part of the voyage while Ahab stays in his quarters. The chief mate is Starbuck, (Leo Genn) a serious, sincere Quaker and fine leader; second mate is Stubb, happy-go-lucky, cheerful and forever smoking his pipe; the third mate is Flask (Seamus Kelly), a thoroughly reliable man who bullies anyone bigger than him. Each mate is responsible for a whaling boat, and each whaling boat of the Pequod has its own pagan harpooneer assigned to it.
Some time after sailing, Ahab finally appears on the quarter-deck one morning, an imposing, frightening figure whose haunted visage sends shivers over the narrator. One of his legs is missing from the knee down and has been replaced by a prosthesis fashioned from a whale's jawbone. A long vertical scar from his hairline down to his chin gives his face a special character.
Ahab orders the crew to gather, and in a rousing speech promises a Spanish ounce of gold to the crewman who first sights Moby Dick. His single, secret purpose for the voyage is hunting down and killing Moby Dick, an old, very large sperm whale, with a snow white hump and mottled skin, that crippled Ahab on his last whaling voyage. The gold coin is nailed to a mast in plain view as a reminder.
In a scene in the Captain's quarters, Ahab explains to Starbuck that over the years he has gathered information on whale presence and migrations from many many whaling ships, and he has fashioned a map that he can use to predict where the whales might be at any time of year. According to his map, Moby Dick should be at Bikini Atoll by the following March.
In another sequence, a whale is sighted, pursued in three small boats, and harpooned. The whale swims away towing the boats, and dives. One of the boats might be towed downwards into the deep, so the rope is cut. The whale eventually weakens as it bleeds, and it is killed. The carcass is cut into pieces, the blubber sliced and the oil rendered in large vats on the vessel. At the end of the work, the seamen celebrate.
Eventually a day comes when Ishmael is given the opportunity to be the lookout from the top of the main mast. It isnt long before he sights a whale, in fact, a large group of whales. The whales are chased, and five of them are killed. The seamen, who will share in the profits from the value of the oil, are happy.
However, Ahab hears from another passing ship that the white whale has been sighted. Immediately he orders a stop to the harvest work, and full sailing in the direction that he believes Moby Dick is traveling, much to the dismay of Stubb and the other seamen, who are shocked that the profit from the whales killed is abandoned.
Only Starbuck offers any resistance to the charismatic but obsessed captain. The first mate argues repeatedly that the ships purpose should be to hunt whales for their oil, with luck returning home profitably, safely, and quickly, but not to seek out and kill Moby Dick in particular and especially not for revenge, as revenge is only for the Lord to take.
Starbuck even dares to show to the other mates a book in which it is clearly written that if a Captain diverts resources to a private matter and neglects the commercial purpose of the enterprise, the other officers are justified in removing the Captain from his duties. However, Stubb and the other mates refuse to go along with even the planning of such an act. Eventually even Starbuck acquiesces to Ahab's will, suppressing his instincts.
The custom of visiting with other whaling vessels met in the open sea is illustrated when the Pequod meets the Samuel Enderby. Captain Boomer (James Robertson Justice) has lost an arm to the whale, comes on board the Pequod for a friendly visit and interchange of news. For Ahab, however, there is but one relevant question to ask of another ship: Hast seen the White Whale? Captain Boomer is stunned at Ahab's burning need for revenge and soon ends their brief interchange.
In another incident that emphasizes Ahabs obsession, when a man accidentally falls off the ship from a great height, he is unusually quick in making the decision that the man is dead and will not resurface. Ahab insists on resuming course without delay, to the dismay of Stubb and the seamen.
Another day, Queequeg is throwing bone pieces on deck in what is evidently a fortune telling ritual. Suddenly, he stares at his bones, says Ah!, and insists on calling the ships carpenter. He places an order for a very long coffin with special carvings, a coffin that is to be pitched and caulked so as to be waterproof. He pays the carpenter, gives the rest of his money, his harpoon, and other property to Ishmael, and stops talking to anyone while just staring vacantly ahead.
Queequeg persists in his catatonic state until much later. When a fight breaks out and Ishmael is in danger of being knifed to death, Queequeg jumps out of his stupor to protect him, and resumes his normal behavior.
Next they meet the Rachel, from which Moby Dick has been seen very recently. As a result of the encounter, one of its boats is missing. The captains youngest son had been aboard. The Rachel's captain begs Ahab to aid in the search for the missing boat, but Ahab is resolute; the Pequod is very near the White Whale now and Ahab will not stop to help. He reasons that he will kill the whale that killed the captains son, and revenge should be the priority.
The man at the mast sights the white whale, and Captain Ahab organizes a ceremony where the man is handed his Spanish doubloon.
In the next sequence the Pequod goes right into a dangerous storm, as the captain refuses to take any course of evasion that would divert him away from Moby Dicks path. Despite extreme danger from strong winds, the captain insists on leaving full canvas on, even trying to replace a torn sail in the middle of the storm. Starbuck begs Ahab one final time to desist on his quest for vengeance, but to no avail. As the ship leaves the storm area, St. Elmos fire appears on the masts, and Captain Ahab shows that he can dominate the elements by his will as he extinguishes the glow from a harpoon he is holding.
The next day, the Pequod meets Moby Dick. The Pequod's crew pursues the whale, which wreaks widespread destruction. Ahab ignores Starbucks pleas one more time, and continues with his ill fated chase. All three boats set out to harpoon him.
Ahab harpoons the whale, but the harpoon line breaks. Moby Dick then rams the Pequod itself, which is heavily damaged. As Ahab harpoons the whale again, the unfolding harpoon rope catches him and he is entangled with other ropes hanging from harpoons that have remained stuck into Moby Dick from previous encounters.
Even stuck to Moby Dick, Ahab stabs and stabs with all his energy trying to kill the whale while it thrashes about, upending the other boats, and diving deep into the sea. After Moby Dick returns to the surface, the crew still on boats see the dead Ahab stuck on the side of the whale, and one limp arm seems to wave, beckoning, even in death, thus fulfilling the mysterious prophecy of Elijah.
Moby Dick destroys all boats. As the seamen struggle to stay on the surface, Moby Dick swims around and around the Pequod creating a whirlpool that catches the ship and draws it down slowly.
Ishmael is on the surface, still swimming, when Queequegs special coffin bobs up from the deep. Ishmael is able to climb on top of the coffin and cling to it for a day and a half, at which time the Rachel comes upon the scene and he is rescued.
Only Ishmael has survived to tell the tale.