In Liverpool in 1860 sailor James Onedin, working for the hard-nosed shipping owner Callon, is desperate to gain a ship of his own and finally acquires the 'Charlotte Rhodes' from drunken old Captain Webster in exchange for marrying the captain's daughter, unglamorous but spirited Anne. He makes his mark when he beats Callon in a race to secure a contract with the Portuguese wine exporter Braganza. His brother Robert and wife Sarah run a chandler's shop, assisted by discontented and frivolous younger sister Elizabeth.

On the return trip from Portugal James teaches Anne the rudiments of navigation. This comes in useful when James and several other crew members become seriously ill, due to rotten meat provided by Robert and which Anne throws overboard. Despite superstitious views that a woman on board brings bad luck, Anne works with the illiterate sailing master Captain Baines to read the charts and brings the ship safely home to Liverpool, where Robert is made to compensate the sick crew and Anne agrees to teach Baines literacy. Elizabeth is torn between two suitors, young sailor Daniel Fogarty and the dandified shipyard owner's son Albert Frazer.

Elizabeth is engaged to Fogarty, who is soon to be made a ship's captain but she is still interested in Albert Frazer. Callon floods James with a load of Braganza's empty wine casks which he is obliged by contract to take but has no room for them. Albert comes to his rescue by offering to store the casks for him and James begins to see that Albert would be a far more profitable brother-in-law than Daniel.

With more barrels than he has room for James needs a warehouse to store them and finds one owned by the widowed Mrs. Arkwright who wants six hundred and fifty pounds for it so that she can return to France and buy a house there. Callon attempts to gazump James but Mrs. Arkwright agrees to sell to James on condition that he takes her to France for free. A rag and bone dealer Ada Gamble is also using the warehouse but is persuaded to leave when it is discovered that she fences stolen property. Robert's wife Sarah gives birth and Anne and James move into the warehouse on the discovery that Webster has mortgaged his house.

James Onedin is in a battle with his former employer and main competitor, Mr. Callan, to keep what few clients he has. Callon has put the squeeze on 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. Callan's son Edmund begins to set his eye on what few assets James has managed to acquire. When Mr. Baines fails to return from a visit to his sister, James knows it has to be Callan's handy work. With Mr. Fogarty away, Elizabeth is at her wits end and Anne thinks she knows what the problem is. Albert Frazer inherits a house and invites not only James and Anne but also Elizabeth, who is the prime reason for extending the invitation.

With James and Robert now aware of Elizabeth's condition, they insist that she reconcile with Mr. Fogarty and marry him without delay. Immediately after Fogarty's return from a sea voyage, they inform him of the situation and he agrees to marry her. Elizabeth has her own ideas however. James faces ruin when the Charlotte Rhodes is abandoned by her crew some six miles from shore due to weather conditions and a fire in the forward hold. Mr. Callon sends his son Edmund on their fastest ship to claim her for salvage. James is desperate - he didn't insure the vessel for this trip - and asks Albert Frazer if his steam-powered ship could get there first. No one is sure what will happen but off they set in what most sailors are calling a teapot.

With a beetle destroying Portuguses vineyards, Senor Braganza asks James to import new vines from Brazil. He sets sail in the 'Pampero', a ship bought by Braganza, who is now his partner for a five year tenure. Worried by the presence of a bullying passenger Dom Vasco, James detours to Baltimore where he strikes a deal with a railroad boss but loses several crew when they decide to join the railroad gangs. He returns to Portugal with his vines having transferred Vasco to another ship.

Michael Adams, an old flame of Anne, visits and James takes him on his next voyage, to Cape Verde to collect coal. Anne travels with them. Michael explains that he has been an outlaw for four years following a death on board ship for which he was suspected of being the killer. George Bethell, a crew member, tells Michael that he is in the clear because the death was logged as being an accident. Albert is too taken up with his new scheme to design steam-ships for a living to listen to Elizabeth when she tries to explain that the baby she is carrying is Daniel's.

A ship James chartered from Callon has been badly damaged but insurance under-writer Chubb will not pay out because it was carrying gunpowder and thus negates the insurance terms. After unsuccessfully trying to compromise Chubb with light lady Kate, James steals back the 'Charlotte Rhodes' from Callon, who has confiscated it as surety. In revenge Callon confiscates Robert's shop, planning to build a dock on its site.

Callon proposes Robert buy another shop from him but Albert points out this would put Robert in Callon's behest and finances another premises. James is charged to take a mysterious passenger to Italy, who turns out to be the revolutionary Garibaldi. Attempts are made by enemies posing as crew members to kill Garibaldi but he shoots them, using his new, six-shooter revolver and is safely delivered.

It appears that a mutiny has occurred on a ship James chartered but the crew explain that there was no mutiny, the captain had gone mad and they were taking the ship over in order to act for the best. James discovers that Kirkwood is indeed mad, a religious zealot, claiming people are out to kill him. He eventually hangs himself after trying to sink the ship and James makes sure that the crew are all acquitted of any mutiny charges.

James has taken emigrants to Australia where he hopes to make enough money to buy off the Pampero by bringing home a cargo of wool, but the sheep-farmers have all left to join the gold rush. He agrees to ferry a load of 'lost souls' from Papua to Victoria for McPherson, a parson, but discovers the parson is actually a slave trader intent on taking the group to the West Indies. After the Papuans have set fire to the 'parson' James returns them to their homes.

Robert lets slip to Albert about the paternity of Elizabeth's child and Callon appoints Daniel a marine supervisor. James is taking emigrants to Canada, including the Stirlings, relatives of Robert's wife Sarah, who, as family members of the Onedins, travel for free. On the voyage out the Stirlings are found to have smallpox and the husband dies. James falsifies the log, allowing the ship to carry on without having to face quarantine restrictions and loss of money. Anne is not pleased.

James is delivering a cargo to the Southern states of America but the Civil War is raging and the North are blockading ports. With him are Anne, who dislikes the idea of helping slave-owning states to profit, and Albert. A nervous pilot is not keen to run the blockade so James decides to run it himself. He is captured by Captain Ferguson, a Northern captain but fortunately for him Ferguson has a great enthusiasm for steam-ships, and, impressed by Albert's plans for a new steam vessel, the 'Golden Nugget', not only allows James to go about his business but defects to join Albert.

To finance the building of a new steam ship James floats a public company pounds worth of shares on the market. However, he is tricked by Callon, who, using other nominees to buy them for him, ends up as the majority share holder and virtual owner of the now depleted Onedin Line, as, to add to James' concerns, Baines, now made up to captain, has lost the 'Pampero' in a storm at Cape Horn. Anne reminds him that he still has the 'Charlotte Rhodes'.