The fine staging of “Dead Man Walking” at Union Avenue Opera, which continues this weekend, begins much as did Opera Theatre of St. Louis’ production of “The Death of Klinghoffer” – namely, at the scene of the crime. Yet while both find their titles and origins in real-life egregious acts, their content envelops a much broader palette of moral uncertainty.

In “Klinghoffer,” the fleeting opening scene shone a stark light on Leon Klinghoffer’s empty wheelchair as shots rang out, and despite controversy surrounding Alice Goodman’s libretto, the initial staging device left no question about the moral turpitude of the murder itself. Similarly, in “Dead Man Walking,” presented with stunning visual and aural appeal by Director Tim Ocel and Artistic Director/Conductor Scott Schoonover, the prologue portrays the barbarous rape and murder of a teenage couple by Joseph de Rocher and his brother.

The legal and moral clarity of the onerous acts in both operas, however, makes what comes afterward make sense. For it is a relatively easy thing to wrap dramatic tension around uncertainty, far less so when the natural tendency is to thumb the perps down, Greek chorus-style, and call it a day.

Yet that’s exactly what Sister Helen Prejean, a Catholic sister serving at an impoverished school in New Orleans, refuses to do when she engages in a penpal relationship with death row inmate Joseph de Rocher. Despite warnings from her colleagues, Prejean visits Joseph at the infamous Angola penitentiary, and assumes the role of his spiritual advisor in the weeks leading to his execution. The experience not only led her to pen the book upon which the opera and 1995 film were based, but initiated her life mission as a fierce opponent of the death penalty.

While this is by no means an easy opera to watch, the score, libretto, performances and staging render the journey an artistically substantial one.

It is our great fortune to hear well-done performances of both John Adams’ score for “Klinghoffer” and Jake Heggie’s for “Dead Man” in less than three months, for at least two reasons. First, both are exceptional compositions. Second, those who lump all modern classical or operatic music into one basket simply are not paying attention. Adams’ insistent percussive ferocity and Heggie’s smoldering lyricality are as different as Mozart is from Brahms.

In writer and multiple Tony-award winner Terrence McNally, Heggie could not have a more formidable partner. His evocation of dramatic tension from the Prejean-de Rocher relationship, as she simultaneously wrestles to save his soul while coming to grips with her own, is something that only a top-notch wordsmith could accomplish.

Elise Quagliata brings her powerful, nuanced voice and acting to the role of Prejean. Her first brutally warm drive from New Orleans to Angola is a literal tour de force, shared briefly by a comical turn from a police officer who catches her speeding but lets her off, remembering the tax audit that followed his past citation of an IRS agent. And her ongoing effort to persuade Joseph that “the truth will set you free” rings both impassioned and emphatic.

Jordan Shanahan is musically bold, belligerent and resonant as Joseph, who thinks refusing an admission will somehow save him. Even his ultimate acceptance of Prejean’s message prior to death leaves us wondering if he would have held the line of denial over moral acceptance if he thought he could squeeze another few months of life out of it.

Neither McNally nor Prejean deny the animosity that inures from victims’ families. The parents of the murdered teens are played and sung with crumbling vengeful certitude by David Dillard, Stephanie Tennill, Cecelia Stearman and Jon Garrett. Deeply moving, too, is the portrayal of de Rocher’s mother as victim, sweetly sung by Debra Hillabrand as she straddles the line of naiveté and knowing acceptance of her son’s evil deeds.

Other fine performances include Robert Reed as the prison warden, and Clark Sturdevant as the morally condescending prison chaplain (“I don’t like that man,” admits Prejean to the warden in a moment of un-sister-like outpouring, but her cognizance only draws her nearer to us). Props also go to Ocel and scenic and lighting designers Patrick Huber and Kaitlyn Breen for creating an arresting visual experience.

The discomfort of “Dead Man Walking” (not to mention “Klinghoffer”) derives from our recognition at some level, even in the face of gruesome reality, that others may not share our perspective. In an era in which preaching to the choir has become all the rage, opening our hearts to the unknown is a precious commodity. Heggie and McNally challenge us to do this, and we don’t go unrewarded from either their efforts or Ocel’s powerful staging.