The play opens during a dinner party at the home of Sir Robert Chiltern in London's fashionable Grosvenor Square. Sir Robert, an esteemed member of the House of Commons, and his wife, Lady Chiltern, are hosting a gathering that includes his friend Lord Goring, a dandified bachelor and close friend to the Chilterns, Mabel Chiltern, and other genteel guests. During the party, Mrs. Cheveley, an enemy of Lady Chiltern from their school days, attempts to blackmail Sir Robert into supporting a fraudulent scheme to build a canal in Argentina. Apparently, Mrs. Cheveley's late mentor and lover, Baron Arnheim, induced the young Sir Robert to sell him a Cabinet secret - which enabled Arnheim to buy shares in the Suez Canal Company three days before the British government announced its purchase of the company. Arnheim's payoff was the basis of Sir Robert's fortune, and Mrs. Cheveley has Robert's letter to Arnheim as proof of his crime. Fearing the ruin of both career and marriage, Sir Robert submits to her demands.