If Nelson Mandela had been Cuban rather than South African, he never would have been awarded a Nobel Peace Prize or become a 20th-century human-rights icon and statesman. Instead, he would have been a “plantado,” one of the political prisoners (the “immovable ones”) who refused to cooperate with the regime in exchange for shorter sentences and lesser punishments.

“Cooperate” meant accepting the re-education and indoctrination program introduced in the early 1960s by Fidel Castro and Che Guevara, then in charge of “La Cabaña,” an 18th-century fortress turned into a prison and execution camp.

For most of the plantados who spent decades in Castro’s cells, there was no redemption, except among some in Cuba’s South Florida exile community. Many in the West, including the self-proclaimed champions of civil rights, were oblivious to the plight of Castro’s political prisoners—often deliberately so.

That’s why Plantados, a new film directed by Lilo Vilaplana, is important. Released recently at the Miami Film Festival, it follows the story of Ramón, a former plantado who escaped and discovers years later that his torturer, lieutenant Mauricio López, is living with impunity with his family in Miami.

Ramon’s discovery takes us back, through his painful memory, to Castro’s prisons, where he suffered the worst tortures and witnessed executions and unspeakable acts of violence against other political prisoners. The punishments included being thrown in sewer trenches, having to stand naked for days in tiny cells shared by four prisoners, where only one could lie down to sleep, suffering routine beatings, watching the humiliation to which their loved ones were subjected when visiting them, and other degrading experiences.

In Miami, Ramón and his family, among them the son of Jorge (nicknamed “the poet” by other inmates), who died in Mauricio’s prison, confront the impossible dilemma: whether to kill Mauricio and avenge their suffering or try to bring him to justice, which probably would yield no result in U.S. courts.

The plantados were known to favor justice over vengeance, but it is one thing to be principled in the abstract and another to have to confront the dilemma in flesh and blood. Vilaplana’s movie presents the spectator with the wrenching gamut of moral dilemmas and psychological drama derived from the plantados’ story.

At one point, the wife of one of the prisoners tells her husband that she and her family are living like pariahs for being associated with counterrevolutionaries, not to speak of the sexual humiliations suffered when entering the prison on visit days.

The story of the plantados and their persecutors also carries long-lasting moral implications for the latter. Mauricio’s family, confronted with details of his shameful past, initially refuse to acknowledge the truth—that is, accept that they have been blind to the atrocities the loving husband and father committed in the past.

And then there is the crucial question of how much responsibility those who served in Castro’s prisons had for carrying out the orders they received. At one point, a corporal who throws the prisoners into the sewer trenches tells one of them, a dissident: “You were part of the victors and ended up with the vanquished . . . and we sided with the communists.” What he is telling him is that in a totalitarian system there is only one way to survive.

Years later Mauricio, confronted by Ramón and his nephew, tells them he was not responsible for setting up the system; he was just following orders: “If it hadn’t been me, it would have been someone else. . . . Now I am with you.”

But the moral of Plantados is that you always have a choice, no matter how narrow the options and how strenuous the circumstances. They opted for resistance knowing it could cost them their lives, as when they drew blood from their own veins to color a piece of tissue red so they could brandish it from their cell’s window, as if it were a Soviet flag, while jeering a visiting dignitary.

Mario Chanes de Armas, who served 30 years in Castro’s cells, died without the world recognizing his heroism. Eusebio Peñalver Mazorra, who endured 28 years of torture, some of it racially motivated because he was black, never got the Nobel Peace Prize—nor will the others who lived to tell the tale and give brief personal testimonies at the end of Vilaplana’s movie. None of them will receive the recognition they deserve.

Vilaplana’s film begins, only begins, to do justice to these immovable heroes.