Florencia Grimaldi, a famous opera diva, is returning to her homeland of Brazil to sing at the Teatro Amazonas in Manaus, in hopes that her lover Cristobal, a butterfly hunter, will return from the Jungle to hear her. She boards a steamboat for the trip down the Amazon, and hides her identity from the other passengers, one of whom is Rosalba, a budding journalist hopeful to interview Florencia and who has compiled information on Florencia for the past two years in a notebook.
When Rosalba's notebook accidentally falls overboard, the captain's nephew, Arcadio, dives in to retrieve it, and Rosalba instantly becomes infatuated with him. A storm forces the ship ashore.
After the storm passes, the ship resumes its journey to Manaus. Rosalba, distraught over her notebook (which was destroyed in the storm) decides to abandon her feelings for Arcadio. Florencia and Rosalba then argue over the importance of the notebook and its contents, and Rosalba realizes that the woman she is speaking to is in fact Florencia herself. Inspired by Florencia's faith in the power of love, Rosalba decides to accept her feelings for Arcadio.
The boat arrives in Manaus but a cholera outbreak prevents the passengers from going ashore. Florencia, in despair over the possibility of never seeing Cristobal again, is magically transformed into a butterfly, so that perhaps she will be reunited with her butterfly-catcher husband.