Series 4

Smuggler Doughty introduces Jack to his supplier, German Captain Bauer, who offers Jack work guarding an air-strip in South America against local tribes. However, on learning that Bauer wants the locals killed for the oil on their land, Jack refuses. Nonetheless, he buys a warehouse full of fire-damaged, bankrupt goods from Bauer, which he and Sarah sell in Gallowshield market. Jack's able to repay Matt's debt and retain a handsome profit, though he's less fortunate in love when Margaret, for whom he has fallen, returns to London to get married.

Jack is visited by former schoolmate, teacher Sid Meek, who is in touch with Bill Pierce, Matt's nephew, now a brilliant law student at Oxford and in financial straits. Sid, secretly in love with Bill, asks Jack to investigate which takes him to Oxford where he meets Bill at a charity ball hosted by Labour philanthropist Violet Laurence, who occasionally pays Bill for 'favours'. Bill, heavily in debt, considers dropping out of his course to take manual work with his girlfriend's father but Jack loans him the money, attracting the attention of Mrs Laurence's niece Imogen Lorrimer, visiting from London.

Jack has been in London for three years with Imogen, but, despite still having feelings for him, she leaves to avoid scandal as her aunt is a standing Labour member for Gallowshield. The Tyneside hunger marchers arrive in town as Jack, tipped off that there is North Sea oil, buys cheap land to sell to the interested company. At a toga party given by Mrs Laurence for the hunger marchers, Jack encounters Jessie, still married to Ashton and with three children, but seeing upper-class socialist Robin Cunningham. She opposes his land deal but Jack buys her silence by threatening to tell Ashton about Robin. Sarah visits, pleased to be part of the deal.

Having made a huge sum from his deal with the oil company, Jack is mixing in London high society. He is sought by his land agent Frank to help broker the sale of an expensive emerald necklace to Morty, Jack's old American colleague, on behalf of wealthy Philip Martin, with a commission for them both. Martin's sister Jane takes a shine to Jack but proves to be unhinged and willing to kill for the necklace. The sale goes ahead and when Jack learns that Morty paid off the mobsters who were threatening him, he waives his half.

Lady Caroline invites Jack to visit her and her family back in Gallowshield. He finds Sarah about to marry agent Stan Liddell, who is involved in anti-fascist politics as the Blackshirts whip up hysteria against Jews. Jack steps in to help persecuted shopkeeper Manny Goldstein before attending a function given by Lady Caroline's husband, Edward Mostyn, who, although he hates fascists, needs to invite their leader Smith-Jameson to improve his chances of candidacy. Jack tells Smith-Jameson what he thinks of him and walks out, supported by socialist guest Tania Corley. Before returning to London, he buys Manny's shop so that, when fascist thugs attack, he forces Smith-Jameson to fully compensate Manny or risk prosecution.

Jack is dating Tania, whose mother, the communist Lady Leamington, has a party to raise funds for the victims of Franco in the Spanish Civil War. At his London practise, Billy treats Bob Randall, son of Jack's old army sergeant Fred, wounded fighting for the Spanish Republicans. Aware that Jack considers himself in debt to Fred, who once saved his life, Jessie and Billy use Fred as go-between in persuading Jack to smuggle guns past Franco's blockade to help the Republicans. With Tania, Jessie – who has left Ashton – Billy and left-wing journalist Nigel Scott-Palliser, Jack sets sail under the guise of a pleasure cruise.

Jack learns that Scott-Palliser plans to have him arrested for gun-running, so he sends Tania home and gets the ship's captain to put ashore elsewhere to avoid the Nationalist gunboat, taking steward Raoul Savory with him. Jessie's shocked to discover that Scott-Palliser has been financed by Stalin's government and plans to give the guns to the Communists and not the Socialists, whom he sees as traitors. Whilst keeping it from him, she and Jack reminisce of old times. Raoul, however, learns of Scott-Palliser's deceit and diverts the Communist convoy, though Scott-Palliser escapes. Jack, Jessie, Billy and Raoul outrun Franco's Moorish cavalry to get the guns to the Socialists but Scott-Palliser lies in wait for Jack.