This novel has a unique structure in that the first chapter is told in the present day from the voice of Dede, the only surviving Maribel sister who reflects back on the past and on her sisters' lives. We learn from the very start that they all have died and that she has lived on to tell their story. This portion of the story is part of the exposition. The exposition establishes the background of the story and the initial conflicts. The next section of the novel establishes the specific exposition of each of the other sisters: Patria who marries and has children; Minerva who goes to school, learns the truth about the dictator, Trujillo's regime and reign of terror, and eventually joins the revolutionary movement against him; and Maria Terese, the youngest, who also joins the revolution with her sister.
The primary conflict of the novel is how the sisters all join together to be a part of the revolution against Trujillo. The novel gives each of the sisters a voice to tell their own story, so we learn in first person narration what each of them is motivated by and how they each see their role in the revolution. Each of the women and their spouses end up risking their lives and freedom for the cause. Only Dede stays away from the operation. At one point, all three of the other sisters and their respective spouses are imprisoned by Trujillo, but they are eventually released.
We are forewarned of the resolution of the novel at the very start of the story. We know that the three revolutionary sisters are all assassinated by Trujillo's men. What is important about the end of the novel though is that even though they died, they died as martyrs to the cause and served as inspiration for others to carry on their work in the eventual overthrow of the terrible dictator. They were called the "mariposa" or "butterflies" as a code name, but it serves as a fitting symbol -- they were transformed from young women, into revolutionaries, into martyrs, but it is Dede's responsibility to continue to tell their story.