"Call me Ishmael," the narrator begins, in one of the most recognizable opening lines in American literature. This observant young man from Manhattan has been to sea four times in the merchant service but yearns for a whaling adventure. On a cold, gloomy night in December, he arrives at the Spouter-Inn in New Bedford, Massachusetts, and agrees to share a bed with a stranger. Both men are alarmed when the bunkmate, a heavily tattooed Polynesian harpooner named Queequeg, returns late and discovers Ishmael beneath his covers. But the two soon become good friends and decide to sail together from the historical port of Nantucket.

In Nantucket, they sign on with the Pequod, Queequeg the more attractive employee due to his excellence with the harpoon. Ishmael, lacking any further ambition, will be a common sailor. The ship's captain, Ahab, is nowhere to be seen; nevertheless, they hear of him. He is a "grand, ungodly, god-like man" (Chapter 16), according to one of the owners, a man of few words but deep meaning, who has been in colleges as well as among the cannibals. A raggedy prophet of doom named Elijah catches the two friends on the dock and hints at trouble with Ahab. The mystery grows on Christmas morning when Ishmael spots dark figures in the mist, apparently boarding the Pequod shortly before it sets sail.

The ship's officers direct the early voyage. The chief mate, Starbuck, is a sincere Quaker and fine leader. Second mate is Stubb, a prankster but an able seaman. Third mate is Flask, dull but competent. When Ahab finally appears on his quarter-deck one morning, he is an imposing, frightening figure whose haunted visage sends shivers over the narrator. A white scar, reportedly from a thunderbolt, runs down his face and, they say, the length of his body. He has a grim, determined look. One leg is missing and replaced by a prosthesis fashioned from a sperm whale's jaw.

Ahab finally gathers the crewmen together and, in a rousing speech, solicits their support in a single purpose for this voyage: hunting down and killing the White Whale — Moby Dick, a very large sperm whale with a snow-white head. Only Starbuck resists the charismatic, monomaniacal captain; the first mate argues repeatedly that the ship's purpose should be to gather whale oil and return home safely. Eventually, even Starbuck acquiesces.