Bert Gibbs, a Cockney plumber, is engaged to Leninia, a political idealist with left-wing views. Because of her politics, Bert is anxious that Leninia does not discover his secret - his father was made a hereditary peer, making him a Lord.

Two con-artists, calling themselves Comrade Curzon and Comrade Howard, are passing themselves off as revolutionaries to attract money from left-wing sympathisers, and have Leninia in their spell. Leninia and Bert argue over Bert's lack of interest in politics.

Meanwhile, a Hollywood actress, Ilya Milona, has hatched a plan with her publicist, Washington Roosevelt Lincoln, to boost her career by marrying an English aristocrat. Learning of Bert's nobility from the devious Curzon and Howard, she invites Bert to her home on a pretence of a plumbing problem, and she and Washington explain their plan: the wedding will be covered by the press, and Lord Thornton-Heath, another aristocrat who will be employed to act the part of Bert's love rival. Bert and his rival will fight and the feud will lead to a heavily publicised divorce.

Bert, depressed after his split with Leninia, is very reluctant, but finally agrees to play his part. Leninia learns of the wedding, and is distraught. She is comforted by Curzon and Howard, who promise to make Bert pay, threatening to kill him.

Meanwhile, Ilya is visited by Bert's mother and, realising her love for her son, she begins to have second thoughts. When Lord Thornton-Heath suggests she marry him instead, they settle on a new plan: Ilya will desert Bert for his rival, freeing Bert from going through with the wedding. Curzon and Howard try to blackmail Ilya to spare Bert's life, but both she and Washington rebuff them, and they are trampled underfoot as the party leave the house.

Leninia rushes to warn Bert about the threat of Curzon and Howard. She finds him and tells him she loves him and doesn't care about his aristocratic secret. The couple are met in the park by Ilya and Washington, who tell Bert, to his relief, that he no longer has to marry. Ilya presents Bert with a cheque for his part in the bargain.

Ilya and her new husband pose for photographs before taking off in a light aeroplane, scattering publicity photos behind them, to the horror of the park-keeper. Bert and Leninia watch them leave clutching the cheque.