Bien que certainement pas aussi populaire que ses opérettes "Babes dans Toyland" (1903), "Mlle. Modiste" (1905), "The Red Mill "(1906), "Naughty Marietta", et "Sweethearts", "Eileen" de Victor Herbert est peut-être son oeuvre la plus sincère et personnelle, et une qui contient beaucoup de ses meilleures chansons (y compris « Thine Alone », « Eileen, Alanna, Asthore » et « The Irish Have a Great Day Tonight »). Rappelons qu'Herbert était né à Dublin, et son opérette traite de la lutte apparemment éternelle menée par les Irlandais pour leur indépendance de l’Angleterre.
Acte I
It is 1798, the year of the brutal uprisings of the United Irishmen, who seek to reclaim their lands from the British. Lady Maude, the attractive widow of Lord Estabrook, an English lady, is the mistress of Castle Sligo, once held by the O'Day family, creating resentment among the Irish locals. Her niece, Eileen, has returned to Ireland after schooling at a convent in France; she is accompanied by the bumbling Sir Reginald. Shaun Dhu leads a band of smugglers and revolutionaries on the Western coast of Ireland that includes Barry O'Day, son of a legendary Irish rebel. The band stores its loot at Biddy's Black Bull Inn in an effort to avoid nasty British tax collector Humpy Grogan. Lady Maude and Eileen stop at the Inn when their carriage breaks down. Barry protects them from some village drunks and flirts with Maude, although it is really Eileen who has caught his eye; Maude is sympathetic to the rebels' cause. Colonel Lester, the local British authority, comes to arrest Barry for treason, but Lady Maude keeps the Colonel at bay, and Barry escapes disguised as Lady Maude's groom.
Acte II
Later, at Castle Sligo, Lady Maude has developed affection for Barry. Eileen explains that Barry is a rogue. Nevertheless, Maude decides to help Barry escape again from the Colonel by putting a coachman's uniform on her guest, Sir Reggie, making him a decoy. Sir Reggie is arrested and sentenced to death before the Colonel learns that he has been fooled and that Barry has gotten away again.
Acte III
By the time of Lady Maude's birthday, Eileen and Barry have fallen in love. Learning that Barry is there, the Colonel has his men surround the castle. Barry surrenders, and he is about to be shot, when news arrives that the King has pardoned the rebels. The arrest is reversed, various couples are united, including Barry and Eileen, and it is declared that "Ireland shall stand among all nations of the world."