The episode kicks off with Frederick Thorncastle (John McCrea), frazzled and desperate, scouring for a last-minute replacement for the regional finals after being sidelined by glandular fever. He eventually settles on Brenda Palmer (Rub-May Martinwood) to step into the breach. Meanwhile, Father Brown (Mark Williams) and Mrs. Isabelle Devine (Claudie Blakley) find themselves in conversation with August Bestwick (David Westhead) amidst one of Brenda's dress rehearsals. Brenda crosses paths with her fellow contestants, moments before Frederick arrives, fashionably late.
As rehearsals begin, Father Brown’s keen eye detects Ron White (Dan Partridge) struggling mightily. Almost immediately, Ron stumbles, bringing Jane Hammill (Lisa Spencer) crashing down with him. Melody Byers (Laura Pigott) initially suspects a mere sprain until she notices that Jane’s shoes lack the appropriate scuffs. Ron insists he had scuffed them the night before and, convinced that Frederick swapped the shoes out of malice, lunges at him. Bestwick decides to call it quits early. Soon thereafter, Ron seeks forgiveness from Father Brown for his outburst. The priest redirects his contrition, advising him that it's Frederick who deserves an apology.
Later that evening, amidst group rehearsals, Brenda heroically shields Frederick from being flattened by a plummeting stage light. The police are summoned when Father Brown concludes that the falling light was no mere mishap. Their arrival is prefaced by Sergeant Goodfellow (John Burton) and Chief Inspector Edgar Sullivan (Tom Chambers). While probing the mezzanine, Devine discovers the tools and matches used to sabotage the light, along with a snippet of purple fabric seemingly caught on a bolt.
During interrogation, Ron acknowledges ownership of the tools. When Father Brown pays him a visit in jail, Ron reaffirms his possession of the tool bag, explaining that he's a handyman by trade. He also confesses his checkered past, marked by frequent jail stints and a deep understanding of criminal activities. It was behind bars that he found faith. Before parting ways, Ron confides in Father Brown, revealing that he overheard Colin Byers (Christopher Jeffers) leveling accusations of cheating against Frederick.
Over a soothing cup of tea, Father Brown, Brenda, and Devine delved into the intricacies of the case, gradually piecing together that only Bestwick and the fellow contestants were privy to Frederick's precise location. This revelation prompted Father Brown and Devine to quiz Colin and Melody about the mysterious light and Frederick’s cheating scandal. Colin firmly shook off any association with Frederick’s near-fatal mishap, while Melody lamented that Frederick should have been disqualified when his former partner succumbed to illness. Adding another layer of complexity, Angela Rippon, alias The Dancing Duchess, serving as the guest presenter, turned out to be Frederick’s doting grandmother.
During Brenda and Frederick’s confidential rehearsal, Father Brown pondered the contradiction: why would Frederick leverage his familial ties to manipulate Bestwick when he was keen on carving a niche independent of his family’s legacy? Their subsequent forced entry into Bestwick’s quarters not only uncovered his residence there but also a packet of matches identical to those discovered in the tool bag. Upon closer inspection, Father Brown deduced that these matches hailed from a homosexual club frequented by Bestwick. Frederick, having stumbled upon this secret after tailing Bestwick one evening, had been using this information as leverage ever since. Bestwick confessed to succumbing to Frederick’s every whim but steadfastly denied any involvement in the attempted assault.
Meanwhile, Melody offered her assistance to Brenda with her dance routine, confessing that her motive stemmed from a guilt-ridden past where she had inadvertently paralyzed her brother during a hastily attempted, under-rehearsed performance. As the rehearsal day drew to a close, Sullivan dropped a bombshell, announcing to the assembled dancers that Ron had been accused of attempting Frederick’s murder.
The next morning, Devine and Father Brown encountered Brenda in the tranquil sanctuary of the church, her eyes filled with fervent prayers for guidance ahead of the recital. Brenda’s nerves got the better of her just as she prepared to take the stage, prompting her to seek solace outside for some fresh air. Devine, unrelenting, reminded her of the pressing schedule and the unprofessional taboo of venturing out in dancing attire. Overhearing this exchange, Father Brown discreetly vanished, just as Brenda stepped into the spotlight.
As Brenda and Frederick grace the stage, Father Brown slips stealthily backstage, confronting Melody with the accusation of attempting to slay Frederick. Despite her alibi of escorting Jane to the hospital before the lighting mishap, his memory brings him back to the sight of her in the foyer, clad in those telltale dancing shoes. Melody persists in her denial of any involvement with the falling light, yet curiosity prompts her to hand over her scarf to Father Brown. Upon inspecting it, he notices a missing fragment of fabric, likely torn when it got caught on the bolt. Confronted with this evidence, Melody caves in, confessing to her scheme to sabotage the light. Her motive? Suspicion that Frederick had tampered with her brother's shoes, as he might have done with Jane's. While Melody unburdens her confession, Father Brown senses that she still harbors one final deception. Despite the embarrassment of halting the live broadcast and making a spectacle of himself, he succeeds in thwarting her last-ditch effort.
Post-recital, The Dancing Duchess confronts Frederick, revealing she has confronted Bestwick about his deceitful tactics and severing ties with him. With the regional spot now vacant, Father Brown proposes Ron and Jane as suitable candidates. The episode concludes on a triumphant note, with Ron and Jane being hailed as the regional champions.
