James Onedin is an ambitious, headstrong sea captain working for the Callon Line. Upon returning to Liverpool in 1860, he is denied a bonus by his employer, Thomas Callon, because a portion of the cargo has been lost. Upon seeing a notice offering the old schooner Charlotte Rhodes for sale, James decides to set up his own shipping company. Unfortunately, his cautious brother Robert, who has inherited their father's chandler's shop while he was away, refuses to put up any capital.^[1]

James calls on Captain Webster to inquire about the Charlotte Rhodes. Webster rejects James' low offer (his life savings), but his compelling spinster daughter, Ann, who deftly manages her cantankerous and drunken father, is concerned about her future. She makes James a counteroffer: the ship as dowry. Anne Webster is significantly older than James, at a time when single women had barely any rights. He offers her an interest in the company, but she insists on the protection that only marriage can bring. He is surprised, but, after some thought, accepts.

He persuades Robert to enter into a partnership (and an equal share of the profits of the first voyage) by giving him all his money. When Ann objects, James explains in private that he is not doing his brother any favour. The money will not last long, and while he is at sea, Robert will have to fend off the creditors and families of his crew.

On the return journey from Portugal, James and Anne appear to be getting on extremely well despite the unorthodox origin of their union. He begins to teach her how to navigate.

A seaman dies and James becomes gravely sick with a fever. Anne has to take over his duties, including navigation. The ship's mate, Mr Baines, is illiterate and cannot help. The crew do not want to take orders or even advice from a woman, but Anne is strong-willed and perseveres despite their growing hostility. She tries to recall and follow James' instructions, but fails to keep the ship on course. Eventually, Baines refuses to heed her instructions any longer.

The strain takes its toll on Anne. Finally, just when things seem to have reached the breaking point, Anne makes a bargain with Baines: she will teach him to read and write in return for his cooperation. They agree to share the responsibilities, and successfully get the ship back on track as James recovers.

When Robert finds out there was no profit on the first voyage, he wants out of the partnership, but is dissuaded by his wife Sarah. James' sister Elizabeth is engaged to Fogarty, but is frustrated by his insistence on getting married only after Callon makes him a captain. She is also strongly attracted to Frazer. James prefers Frazer as well, as his family would be very useful for the newly established Onedin Line.

Callon floods James with barrels, which he is by contract obliged to take in, but he has no place to store them nor money to rent one. Frazer offers temporary storage for free.

With more barrels than he has room for, James seeks a warehouse to store them, and finds one owned by the widowed Mrs. Arkwright. However, she wants £650 for it, more than James can raise. James persuades his reluctant brother to get information from Mrs. Arkwright's unpaid companion, Miss Simmons, who misinterprets Robert's interest in her. Guilt-ridden, Robert extracts a promise from his brother to find her suitable employment if Mrs. Arkwright does leave.

Mrs. Callon learns of James's plan and offers £700 for the building, but James plants doubts in Mrs. Arkwright's mind as to Callon's sincerity. She agrees to James's offer: a house in her French hometown and free passage there. A rag and bone dealer, Ada Gamble, is using the warehouse, but she is pressured into leaving when James discovers she has sold stolen candlesticks to Anne. Robert is aghast when he finds Miss Simmons working for Ada; James shrugs off his outrage.

Robert's wife Sarah gives birth. Anne and James move into the warehouse after Captain Webster mortgages his cottage, where they are living, and Callon forecloses.

James Onedin is in a battle with his former employer and main competitor, Mr. Callon, to keep what few clients he has. Callon pressures Mr. Watson, who recently consigned a small shipment to Onedin, telling him they will refuse to carry his trade to India unless they get 100% of his business. Callon's son Edmund begins to set his eye on what few assets James has managed to acquire. When Baines fails to return from a visit to his sister, James knows it has to be Callon's handiwork. He finds and rescues the shanghaied Baines.

With James and Robert now aware of Elizabeth's condition, they insist that she reconcile with Fogarty and marry him without delay. Upon Fogarty's return from a sea voyage, they inform him of the situation. However, he insists on consulting Elizabeth. Elizabeth stubbornly refuses to be pressured into marriage.

James and Anne finally move into a real house of their own (for £25 per year).

When James sees Braganza in Portugal, he learns that his best client may soon be out of business. The 'devastador' beetle is ravaging the grapes of Europe, and the vineyard next to Braganza's is already infested. He hopes to graft the roots of resistant North American grapes, but has been unable to charter a ship to get them. The only available suitable one is the clipper Pampero.

James proposes a bold plan: that the two buy the ship and its cargo. In exchange for Braganza putting up the money, he will get his grape roots for free and half the profits on the ship's voyages for the next five years, unless James can buy him out before the five years are over. If he cannot, Braganza will get full ownership of the Pampero.

On the voyage, unfavourable winds and troublesome passengers make James decide not to go to Pernambuco to deliver his cargo, but straight to Baltimore, United States. Avoiding a monopoly of salt traders, he makes a deal with a railroad builder: the salt portion of his cargo at a vastly reduced price in exchange for the railroad workers collecting 100,000 of the grape roots that grow like weeds in the region.

James has made enough profit from the trip to Baltimore to pay off the mortgages on the Charlotte Rhodes and the warehouse. He returns to find Anne chatting with Michael Adams, her close friend since childhood who went to sea four years previously. James becomes jealous, and not without reason. It turns out the pair had planned to marry after Adams returned, but he did not, nor did he write.

James charters the clipper Maisie Anges from Callon to pick up a cargo in Gibraltar (for which he mortgaged the cargo of the Charlotte Rhodes). On the return journey, the captain picks up all sorts of goods, including gunpowder, which blows up and sinks the ship. This time, James has insured ship and cargo, but Mr. Chubb of the insurance company claims it's invalid because there should have been a separate insurance for the gunpowder.

Assuming that the Onedins are broke, Callon pressures Robert to sell his shop (which stands in the way of his plans for a new dock); but when Robert mentions that the Onedin Line is a limited company, Callon's son explains that in a limited company the liability of its directors (being James and Robert) is limited to the amount of its share capital. If Callon sues, he bankrupts the company, but not James and Robert. Also, the possessions of the company will be divided among the creditors, and he assumes that James will have made sure the biggest debtor will always be his other company, Onedin Warehousing.

So Robert doesn't sell the shop and Callon decides not to sue, assuming James will not accept bankruptcy, but keep on fighting, even though he no longer had the means to do so. And indeed he does, but he acquires the means by 'stealing' the Charlotte Rhodes and sails off with several hundred pounds he collected from friends and family (plus £100 from a money lender, causing him to sigh "I never signed my life away before").

James gets an offer to take aboard a passenger in complete secrecy for the high sum of £100. This makes him suspicious and through further inquiry he learns that Callon had turned down an offer of 300 guineas, after which he easily manages to raise the price to £400 (£200 up front and £200 on arrival). This is music to the ears of Robert, who has sold his shop to Callon after all and now needs several hundred pounds to buy a new shop (plus stock).

Baines is taken sick and pretty soon a replacement ship's mate presents himself, who says he can quickly gather a crew he knows well. At sea, the passenger hands over orders to take him to Sardinia instead of Livorno, the destination of the ship. The passenger claims the orders are from George Pelham of the foreign office, but they are unsigned. When an 'accident' happens that could have killed the passenger, he reveals his identity – he is Giuseppe Garibaldi, on a mission to oust the occupying forces of Austria and France from Italy.

A discussion arises between James, who wants to reach Livorno in time to collect his bonus (the only profit he can make on the type of cargo he is carrying) and Garibaldi, who is not sure of the welcome he will receive there and wants to land in Caprera, just off Sardinia. The crew, who turn out to all be in on the assassination attempt, decide to try to take over the ship, but fail, in part thanks to the revolver that Garibaldi carries – after each shot they think he is unarmed because he would have to reload. After this, James decides to drop Garibaldi off in Caprera.

There has been a mutiny on a ship chartered by James and he boards off the French coast to see if he can still rescue the cargo of pineapples, which would perish if the crew were to be tried in France. He proposes to sail the ship home under his command and convinces the crew that it is better for them to get a trial in England, so they will be able to see their wives and children again.

They claim they didn't mutiny but relieved the captain of his duties because he had gone mad, throwing food overboard, making false accusations and beating someone for not singing a hymn properly. During the voyage, James finds out the captain is a religious fanatic who is convinced he will die on the voyage. He says the crew plan to kill him and is found hanged shortly after.

James has sailed to Australia with passengers, hoping to get a cargo of wool that will make him over £1000, enough to pay off the Pampero. But once there, he finds the farmers have all left their farms for a gold rush and there is no wool.

This episode plays almost entirely in England. Callon offers Daniel a 'shore job', taking over several of his own duties, as marine superintendent. On the first birthday of Elizabeth and Albert's son William, Robert accidentally reveals that Daniel is the father.

James takes emigrants to Quebec, for £5 a head (food included, since they are by law no longer allowed to take their own). Robert puts some poor relatives on the ship for free, pointing out a clause in the articles of association (which James himself put in there), that family of company owners are always granted free passage on Onedin Line ships. These relatives, however, have small pox, for which there is no cure.

James gets an offer to supply the southern states during the North American civil war. For this, he has to run a Yankee blockade, but the profits would be proportional. He decides to put all the company's money (£2500) into boots, blankets and firearms. On the return trip, he can make another huge profit on cotton, which is in very short supply in England and dirt cheap in the southern states, also due to the blockade.

Anne strongly objects to this support to slavery, but comes along anyway, as does Albert Frazer, leaving Elizabeth behind. They pick up a pilot in Bermuda, who, for £750, will take them to Wilmington, around the blockade, dangerously close to the shore. They succeed, but once there, the pilot says he wants to wait for several weeks before returning because the yanks now know they're there.

The Onedin Line now owns £27,484/10/4 in assets. But that's not cash in hand and James needs £1500 to pay off the Pampero. Robert and Sarah are, however, overjoyed with the £200 dividend they get from their 15% stake (for which they originally invested £15).

James has no intentions of letting Albert build the Golden Nugget – that was clearly just a story to get out of a difficult situation. Albert is in financial trouble now, but Elizabeth sweet-talks his father to take him back into his business and consequently arranges a dinner party designed to get them and James to talk business. Albert explains the economics of a steam ship. Sailing ships have reached their limit in size, but steam ships can be made much larger. A big one would cost £40,000, the price of four clippers, and £1000 in coal for a round trip to Quebec, but it would carry the same cargo as two clippers (2500 tonnes) and do the round trip in 28 days instead of 52.

James orders a 4000-tonne ship, for which he floats a public company with £100,000 worth of shares (£60,000 for building the ship and £40,000 for operating costs). Albert gets 15%, but James is to own the ship. £50,000 will be on call, so with an investment of £20,000 he will control the company because shareholders always disagree (or so he is told). But Callon buys a majority through different nominees (so James won't know what's happening) and manages to sway the other shareholders into electing him as director.