The narrative begins on a snowy evening before Christmas in the quiet valley town of Oakwood, where Katherine arrives only to find herself stranded and unable to recall her friend Nyoda's name. Guided by instinct and fortune, she climbs a hill to what she believes is Nyoda's house, only to discover an empty, seemingly haunted dwelling. Inside, she encounters a mysterious, paralyzed fourteen-year-old girl named Sylvia, who lives there with her overworked aunt and pretends they inhabit a royal palace to escape their harsh reality. Katherine intervenes, builds a fire, and stays until the aunt's employer arrives with news of an accident. Nyoda eventually arrives, rescues Sylvia, and brings her to Carver House for Christmas, where a merry party of friends has gathered.
As the festivities unfold, the young people's curiosity is sparked by legends of a secret passage and an iron-shuttered window in Uncle Jasper's old study. Finding the dead man's diary reveals a tale of youthful friendship between Jasper and his lifelong friend Tad, which was shattered when both fell in love with a celebrated singer named Sylvia Warrington. Tad won her hand, prompting Jasper to seal the window facing his former friend's house and to fill his life with ancient history. Later misfortunes ruined Tad's medical career, and both he and his wife seemingly died in Cuba.
Meanwhile, strange events occur at Carver House, including bloody footprints on the stairs and an uninvited visitor who uses a hidden tunnel leading from a cave beneath the hill. The mystery deepens when the young people become trapped in the subterranean passage and are mysteriously released. The narrative reaches its emotional peak when an unopened letter reveals Tad's innocence in the historical medical tragedy, prompting a frantic search. The climax brings Tad back to Oakwood just as Sylvia's true identity as his daughter is uncovered, and a miraculous emotional recovery restores her ability to walk, culminating in a joyful celebration of reconciliation and new beginnings.
