The Mirabal sisters, especially Minerva, are restless on their farm. They want to get out into the big world and see what there is to see. Lío comes into their lives and presents them with the possibility of joining the revolution. This anticipation of the future (mixed with lack of fulfillment and a lot of frustration) matches right up with the first stage of the classic tragedy plot.
In a tragic dream stage, the hero becomes committed to the course of action, and things go well for a while. In In the Time of the Butterflies, the three butterfly sisters have committed to the revolution and things are going swimmingly. After Fidel's victory in Cuba they feel sure that they will succeed in overthrowing Trujillo. Everyone has his or her part to play.
Minerva, Mate, and Patria attempt to convince Dedé to join them but she won't, blaming her indecision on her husband, Jaimito. This is just one example of the frustration stage, where things start going wrong. Another aspect of this stage is the "shadow figure," which could very well be Trujillo in this case.
Mate and Minerva are put into prison, Patria loses her land and son, and all three of the girls' husbands are jailed. There is very little hope. (This is called the "Nightmare Stage" for a reason, folks.) Things are out of control and the walls are closing in.
A tragedy generally ends in lots of death and destruction, and In the Time of the Butterflies is no different. Patria, Minerva, and Mate foolishly ride together to visit the prison in Puerto Plata, even though Dedé warns them against it. They are ambushed and murdered.