In 1968, a vivacious Catholic schoolgirl named Deloris Wilson was far more passionate about singing than mastering Latin verbs, much to the displeasure of her nun instructors. Fast forward to 1992, and Deloris has evolved into Deloris Van Cartier, a glamorous lounge singer dazzling crowds in Reno, Nevada's elite venues, supported by her wealthy, albeit married, mobster boyfriend, Vince LaRocca. However, when Vince presents her with an ostentatious gift, Deloris attempts to return it, only to witness his brutal murder of an informant, immediately placing her own life in jeopardy as she becomes the target of his wrath.
In a desperate bid for safety, Deloris seeks refuge with the authorities and is placed under the protection of Police Lieutenant Eddie Souther. He decides that the safest hiding spot for her is the struggling convent of Saint Katherine's Parish in a decrepit area of San Francisco. Disguised as "Sister Mary Clarence," Deloris finds it challenging to adjust to the convent's strict, somber environment. However, she gradually forms friendships with her fellow nuns, including the lively Sister Mary Patrick, the dryly humorous Sister Mary Lazarus, and the quiet Novice Sister Mary Robert.
As the convent prepares for Sunday Mass, Deloris, utilizing her vast musical knowledge, cannot resist stepping in to rejuvenate their dull choir performance. Initially, the Reverend Mother, portrayed by Maggie Smith, is horrified by the dramatic change, yet Deloris' infectious passion eventually wins her support, and she takes on the role of choir director.
As time goes on, Deloris leads the nuns in an innovative blend of gospel, rock, and roll, electrifying their performances and infusing them with enthusiasm. Despite the Reverend Mother's early skepticism, Monsignor O'Hara recognizes the choir's revitalized approach, which not only draws a lively crowd to their services but also breathes life into the community.
However, trouble looms when Souther admonishes Deloris for nearly exposing herself on live television, a consequence of Vince's malicious scheme that has placed a bounty on her ahead. She reassures him that she will maintain a low profile. While Souther attends a solemn Mass for reflection, the choir continues to enthrall congregants with gripping renditions, including a clever adaptation of "My Guy," recently reworked as "My God," impressively showcasing their harmonious voices.
As news of the choir's astounding success reaches the ears of the Vatican, Pope John Paul II plans a visit to the church, throwing the Reverend Mother into a frenzy of preparations. Deloris confides her concerns about Vince's pending trial and her intention to leave once it concludes. In a twist, the Reverend Mother admits she feels inadequate to modernize the convent, having decided to step down as abbess. Deloris counters her resignation, highlighting the necessity to preserve the vitality of the parish, but the Reverend Mother remains unyielding.
Meanwhile, Souther uncovers a corrupt detective in his department who has disclosed Deloris' whereabouts to Vince, prompting him to rush back to warn her. Unfortunately, before he can arrive, Vince's henchmen abduct both Deloris and Mary Robert, who finds solace in Deloris' guidance amidst the chaos. As they plan their escape, the Reverend Mother divulges to the nuns that Sister Mary Clarence is indeed Deloris Van Cartier, just as she formally resigns from her position.
Empowered by this revelation, the nuns devise a bold plan to rescue Deloris. In a breathtaking chase over Reno, Vince commands his men to dispose of Deloris, yet they hesitate at the sight of her nun's habit. The nuns arrive at Vince's casino, but they find themselves cornered in the lounge.
As tension escalates, Deloris readies herself for a selfless sacrifice. At the crucial moment before Vince can pull the trigger, Souther interjects, shooting Vince in the arm and apprehending all involved. Grateful for Deloris' bravery, the Reverend Mother ultimately decides to continue leading the convent.
Back in San Francisco, the choir, now empowered under Deloris' leadership, performs a powerful rendition of "I Will Follow Him," captivating a packed audience at the renovated Saint Katherine's. The spectators erupt into adoration, with even the Reverend Mother, Pope John Paul II, Monsignor O'Hara, and Souther joining in with a standing ovation. Deloris continues to inspire and guide the choir as they embark on an exhilarating musical journey, strengthening their unbreakable bond through shared passion and purpose.
