Secret Beyond the Door

New York heiress Celia Barrett is poised to marry her lawyer Bob Dwight, but he urges a last, clear-eyed check. He convinces her to take a vacation in Mexico with her friend Edith Potter, hoping distance will reveal her true feelings.

During the Mexican trip, Celia falls in love with American architect Mark Lamphere and they marry shortly thereafter. The romance overturns her engagement with Bob and sets the stage for a shocking turn in her life.

In their honeymoon, Celia playfully locks Mark out of their hotel room. Mark becomes cold and abruptly leaves for urgent business, promising Celia she will follow later and handle arrangements.

Five days later Celia arrives in Mark's hometown, Levender Falls. Mark is away on business, and his sister Caroline greets Celia at the train station and escorts her to Blade's Creek, the family estate.

Celia learns Mark is a widower with a teenage son, David. Caroline and Miss Robey oversee David, with Miss Robey wearing a scarf to conceal a facial scar, a secret they guard to protect appearances.

At a party, Mark unveils six rooms he built in a mansion wing, each recreating a notorious murder scene with female victims. A seventh room is locked and he refuses to show it, hinting at a dark secret.

Miss Robey accidentally reveals her full face to Celia and confesses she had plastic surgery to remove a scar. The Lampheres keep the truth from others to protect her, and Celia realizes Robey resents her for marrying Mark.

Celia secretly enters the seventh room, discovering it is a replica of her own bedroom and infers that Mark intends to murder her. Overwhelmed with fear, she flees the house to escape his perilous obsession.

Mark, torn between love and an overpowering urge to kill, struggles to suppress his homicidal impulses. Celia returns because of her love, while Caroline plans to take David to New York and Miss Robey is fired, leaving the staff away and increasing the risk.

To protect Celia, Mark leaves, but his impulse draws him back. They discover smoke as Miss Robey—believing Celia is alone—has locked them in and set fire to Blade's Creek. Mark pries open the door and they flee the burning mansion.

After escaping, the couple resumes their honeymoon in Mexico. Mark tells Celia that she has killed the root of the evil in him, implying their bond has endured beyond the danger.