Within a Tyrolean castle in the late 18th century, the de Berghmann line begins with twin sons: Baron Gregor de Berghman [Boris Karloff] and Anton de Berghman [Boris Karloff]. An old prophecy shadows the family: the younger shall kill the elder in the Black Room, a fate that gnaws at the heart of the castle’s rulers. The elder Bar on Gregor de Berghman, [Henry Kolker], rules with a dark hand, amplifying the fear that the prophecy might come true, while the fatherly concern of Baron de Berghman grows as the years pass.
Years later, in 1834, the tale tilts toward tragedy and tension. Gregor has become a depraved ruler who murders the wives of local peasants, leaving villagers to tremble at the mere mention of his name. His twin Anton, who cannot use his right arm and has spent much of his life traveling across Europe, returns to the fortress with a gentler presence that starkly contrasts his brother’s cruelty. The returning Anton wins the affection of the staff and the villagers alike, becoming a beacon of warmth in a place grown cold under Gregor’s shadow. Thea Hassel, [Marian Marsh], daughter of the loyal adviser Colonel Hassel, finds herself drawn to Anton, yet her heart also wavers toward Lt. Albert Lussan [Robert Allen], who is loyal and steadfast, a man who sees through Gregor’s veneer and believes in a future free from tyranny.
As Gregor’s schemes unfold, Mashka, Mashka [Katherine DeMille], a servant, disappears after being seen in the baron’s vicinity, and suspicion quickly ignites a chorus of fear and anger among the villagers. A mob descends on the castle, demanding answers and change. In a dramatic pivot, Gregor agrees to abdicate and transfer power to his popular brother, with papers signed to relinquish the baronetcy to Anton. Yet the moment of supposed reconciliation becomes a carefully laid trap: Gregor lures his unsuspecting brother to the Black Room, murders him, and casts him into a pit where the bodies of Mashka and other victims lie, a grim chorus line that confirms the prophecy’s chilling inevitability. Gregor now assumes Anton’s identity and sets his sights on wed Thea, a union that would cement his control. Thea’s father, Colonel Hassel [Thurston Hall], supports the match, while Lt. Lussan’s objections burn bright as a warning signal of the deception to come.
In the wake of the murder, Lt. Lussan’s faith in justice leads him to resist Gregor’s rise. The baron’s deceit is grievously exposed when Gregor murders Colonel Hassel after a tense game of chess and a mirror reflection that reveals the impostor’s true face. The Lieutenant is framed and condemned to die, a cruel twist that underscores the fragility of law in this house of shadows. Yet even as the system falters, Anton’s loyal mastiff senses the ruse, recognizing that the man posing as Anton is not their master. The dog becomes a silent ally, pursuing Gregor into town as the wedding to Thea proceeds.
In a parallel drama, Lt. Lussan escapes his cell and joins Thea as she urges him to flee. He chooses to stand and face the tide, while the wedding ceremony in the town cathedral unfolds with solemn ceremony and a warning in the air. The priest’s words—> speak now or forever hold their peace —hang over the congregation as the dog attacks the mistaken groom, revealing the impostor’s concealed identity and forcing a confrontation that exposes Gregor in the middle of the holy rite. The townspeople surge like a living riot, driven by fear and a desire for rightful order.
Gregor, now desperate, seeks refuge in the Black Room, but the mob converges. The mastiff squeezes through the secret passage, and the chase culminates with the dog pouncing on Gregor, who tumbles backward into the pit and onto the blade still clutched by his murdered brother’s hand. The brutal fulfillment of the old prophecy concludes the tale with a grim, inevitable justice: Gregor is undone by the very trap that the prophecy foretold, and the castle’s curse ends as the crowd carries the memory of Anton and the fate of a family torn by ambition and betrayal.
