The opera's plot begins with Treemonisha, a young woman raised by her grandmother, being expelled from her school for teaching advanced arithmetic to her classmates. She returns to her community, where she finds that the people are living in poverty and are being oppressed by a corrupt leader named Remus. Treemonisha uses her education and knowledge to help the people, and she eventually leads them in a rebellion against Remus.
The opera's music is a blend of African-American folk music, classical music, and ragtime. Joplin uses various musical styles to create a unique and evocative sound. The opera's themes are also explored through the music, with Joplin using spirituals and other traditional African-American music to convey the characters' emotions and experiences.
Treemonisha was not performed during Joplin's lifetime and was not widely known until the late 20th century. It has since been performed and recorded by various opera companies and orchestras, and it is now considered an important work in American music history.