The scene of the opera is laid in Portugal and Africa, and the first act opens in the council chamber of the king of the former country.  Inez, his daughter, is mourning the long absence of her betrothed, Vasco di Gama the explorer.  Her father, wishing to marry her to Don Pedro, the President of the Council, tries to persuade her that Vasco has perished by shipwreck; but the refutation of the story comes in the sudden appearance of Vasco himself, who is summoned before the Council and narrates to them his discovery of a strange land, producing two of the natives, Selika and Nelusko, as confirmations of his announcement.  Don Pedro incites the inquisitors to deny the truth of the story, at which Vasco breaks out in such a furious rage against them that he is arrested and thrown into a dungeon.  The second act opens in the prison, where Selika is watching the slumbering Vasco.  As he wakens she declares her love for him, and at the same time saves him from the dagger of the jealous Nelusko.  She also indicates to him the course he should have taken to discover the island of which he is in quest.  To save her lover, Inez consents to wed Don Pedro; and the latter, to cheat Vasco of his fame, takes command of the expedition under the pilotage of Nelusko, and sets sail for the new land.  The Indian, thirsting for vengeance, directs the vessel out of her course towards a reef; but Vasco, who has followed in another vessel, arrives in time to warn Don Pedro of his danger.  He disregards the warning, distrusts his motives, and orders him to be shot; but before the sentence can be carried out, the vessel strikes and is boarded by the savages, who slaughter the commander and most of his men.  The fourth act opens on the island which Selika pointed out on the map, and of which she is queen.  To save him from her subjects, she declares herself his spouse; but as the marriage rite is about to be celebrated, Vasco hears the voice of Inez in the distance, deserts Selika, and flies to her.  In the last act, as the vessel sails away bearing Vasco and Inez back to Portugal, Selika throws herself down under the poisonous manchineel-tree and kills herself with its fatal flowers; expiring in the arms of Nelusko, who shares the same fate.

The first act opens with a very sweet but sombre ballad sung by Inez ("Del Tago sponde addio"), which recalls the English song, “Isle of Beauty, fare thee well,” and is followed by a bold and flowing terzetto.  The third scene opens with a noble and stately chorus ("Tu che la terra adora”) sung by the basses in unison, opening the Council before which Vasco appears; and the act closes with an anathema hurled at him ("Ribelle, insolente"),—­a splendid ensemble, pronounced in its rhythm and majestic in the sweep of its passionate music.