Israeli actor, writer and director Ami Dayan delivers a stunning, overpowering performance in the New Jewish Theatre’s production of “Conviction.” He portrays Rev. Gustave Gonzalez, a Roman Catholic priest during the Spanish Inquisition who falls in love with, and secretly marries, a Jewish woman.

Dayan, a native of a kibbutz in northern Israel, also portrays a Spanish investigator in a 1960s play-within-a-play, who is interrogating an Israeli genealogist caught stealing the complete file on the notorious and tragic case from the Spanish Archives in Madrid in 1962, during the regime of the fascist Falangist dictator Francisco Franco.

Dayan moves seamlessly back and forth between the Medieval Spanish priest and the modern Spanish interrogator throughout the entire 90 minutes of the production, which has no intermission. The part is demanding not only in terms of dialogue, but also in its sheer physicality. As the lead character, Dayan is hurled about the stage by his conflicting emotions, trying on the one hand to remain faithful to the Catholic Church, while at the same time honoring the love he feels for the Jewish woman Isabella, who instantly captivates him with her dark and soulful eyes. He learns to “be a priest by day and a Jew at night,” but must pay a heavy price for his double-life.

“Conviction,” by Oren Neeman, one of Dayan’s fellow kibbutzniks, is based on the Israeli novel “Confession,” by Yonaton Ben-Nachum, who was one of Neeman’s teachers. The play was adapted from its original Hebrew into English by Dayan, and had its world premiere in Denver in 2007 (Dayan has been associated with the Boulder Museum of Contemporary Art for the past 14 years). The play has received critical and audience acclaim in numerous productions throughout the nation.

The play has been structured in some productions with a three-person cast, but in the “talk-back” with the audience after the show, Dayan said he believes it works best as a one-person drama. He is absolutely right. So skilled and nuanced is his performance, which is nimbly directed by Joe Gfaller, who re-staged the production works superbly with a one-person cast. Its back-and-forth between the tormented priest and the tormenting Spanish interrogator are consistently smooth flowing and never distracting from the powerful narrative thrust.

The relationship between the “modern” story of the Israeli scholar who is caught stealing the file on the Gonzalez case, and the Medieval facts of the tormented life, arrest and death of the priest and his Jewish wife, are clarified during the course of the play. The strong dialogue is laden with symbolism and Jewish references, which are likely to challenge the audience and enhance the theatrical experience. It is a complex story, but in the capable hands of Dayan and Gfalller, it is made accessible to all.

Kudos are deserved by the entire production staff, with a special shout-out to lighting designer Nathan Schroeder, whose work is stunning in key points of the play. The spare set, with the well-worn desk of the Spanish interrogator, and the large stained glass window depicting the crucified Jesus, provide vivid visual enhancement to the dialogue.

Dayan is making a kind of “homecoming” to St. Louis during the run of “Conviction.” His father, Amatzia Dayan, had been the Israeli shaliach, or emissary at the Jewish Community Center in 1970-73, when Ami attended school in town. Indeed, his tour-de-force performance is one that St. Louis audiences should not miss.