In turn-of-the-century Buffalo, Edith Cushing, an aspiring author who prefers writing ghost stories to romance, rejects the
marriage proposal of her childhood friend, Dr. Alan McMichael. Instead, she becomes captivated by Sir Thomas Sharpe, a charismatic English baronet seeking investors for a revolutionary clay-mining machine. Edith's wealthy father, Carter Cushing, fiercely disapproves, offering Thomas and his enigmatic sister, Lucille, a bribe to leave America. Shortly after, Carter is brutally murdered, leaving Edith devastated. Seeking solace and believing in Thomas’s genuine affection, Edith marries him and relocates to Allerdale Hall, their crumbling ancestral mansion in Cumberland, England, which sits atop a treacherous, shifting mountain of red clay that bleeds through the floorboards.At the remote estate, Edith quickly realizes the harsh reality of her new life. Lucille is coldly unwelcoming, and the massive house is steeped in oppressive gloom and decay. Edith begins seeing terrifying, bleeding phantoms that whisper cryptic warnings about "Crimson Peak." Unnerved, she uncovers dark
family secrets: Thomas is heavily indebted and has a history of marrying wealthy heiresses under false pretenses, only for them to die mysteriously from poisoned tea shortly after transferring their fortunes. Lucille, consumed by a deeply disturbed, incestuous obsession with her brother, has been his willing accomplice, eliminating every past wife and even murdering their abusive mother.Realizing she is the next target as Lucille poisons her tea, Edith grows desperately ill and weak. Meanwhile, Dr. Alan McMichael, having discovered suspicious details about Carter Cushing's death and Thomas's fraudulent past, travels all the way to England to rescue her. Alan arrives at Allerdale Hall just as Lucille's murderous plot reaches its climax. Upon discovering Alan, Lucille viciously attacks him, stabbing him repeatedly, and forces Thomas to finish him off. However, Thomas's genuine love for Edith has grown, and he refuses to deliver the fatal blow to Alan, finally rebelling against his sister’s tyrannical control.Enraged by his betrayal, Lucille betrays Thomas, stabbing him to death in a fit of jealous fury. Edith, fighting for her own survival, manages to overpower Lucille during a brutal, desperate struggle in the snowy courtyard, ultimately killing her with a shovel. As the ghosts of Lucille and Thomas’s previous victims look on peacefully, Edith is rescued by a recovering Alan. Leaving the cursed, bleeding mansion behind forever, Edith embraces her survival and returns to America, finally finding her voice as a published author whose darkest ghost story is now grounded in terrifying, hard-earned reality.