It tells the story of two contrasting realities in the early 20th century: The construction of a railway in the Amazon rainforest and the glamorous life of Rio de Janeiro, where politicians and big businessmen lived. Consuelo is a young pianist heading toward the Amazon with her husband, Alonso. On the way, the two have an accident, and Alonso ends up losing his life. Alone and helpless, Consuelo gets lost in the middle of the forest, being weak and very sick. However, she ends up being supported by Joe Caripuna, a local Indian who welcomes the girl. The two become great friends, and Joe falls in love with the girl. He takes her to live around the railroad workers' camp, where she meets Dr. Richard Finnegan, who takes care of her health and all the workers who were in a dramatic situation. Richard also falls in love with Consuelo, who repays love, but the difficulties of work and the situations in which they find themselves make it difficult for them to get closer.
A inicios del siglo XX, en el corazón de la floresta amazónica, una carretera de fierro es construida para cortar la selva y poder llevar por sus carriles prosperidad a una región inhóspita. El ambicioso proyecto atiende a intereses políticos y les costará la vida a trabajadores de todo el mundo envueltos en la construcción. Recién llegado de los Estados Unidos, el joven médico Richard Finnegan se deslumbra ante la belleza de la selva, pero se pasma al conocer las precarias condiciones de trabajo de los operarios y las enfermedades tropicales que quitan la vida de muchas personas. En medio del horror y de los chantajes políticos que imposibilitan la construcción del ferrocarril, Finnegan conoce a la joven pianista Consuelo, rescatada de la selva a las puertas de la muerte, y se enamora de ella. Mad Maria muestra el drama de los hombres que sobrevivieron al horror en la selva y la historia de amor que se inicia a las márgenes del ferrocarril, en medio del caos de la selva.
Em meio à história da construção da ferrovia Madeira-Mamoré, no norte do Brasil, um dos maiores desafios arquitetônicos do início do século XX, um médico se apaixona por uma paciente com um passado trágico.
