The film opens with an eerie inscription: "When I die, Bury me deep, Lay two speakers at my feet, Wrap some speakers around my head, And rock and roll me." From this unsettling note, we enter the world of Red Miller, portrayed by Nicolas Cage, a lumberjack working in the serene woods. After wrapping up his day, Red leaves via helicopter, and we shift to his wife, Mandy, played by Andrea Riseborough, who is engaged in sketching fearsome animals while enjoying some marijuana.
As Red returns home, their conversation dances among topics of planets, stars, and even the Marvel character "Galactus." The film then reveals a montage highlighting their love, showing them at a picturesque lake and gazing at each other through the flames—suggestive of an impending doom looming over them. One fateful day, Mandy ventures into the woods, where she discovers a lifeless fawn, a profound symbol of their innocence lost. She narrates a troubling incident from her youth, where she felt pressured into killing a starling, reflecting her internal fears.
Mandy's unease heightens as she reads a dark fantasy novel, and her worries materialize when she crosses paths with a sinister truck containing Jeremiah Sand, a man played by Linus Roache, who becomes dangerously fixated on her. Jeremiah's obsession intensifies, leading him to devise a nefarious plan with his followers, Brother Swan and Sister Lucy, who call upon a gang of grotesque, satanic bikers. Their sacrificial demands echo ominously, as they chant, "Blood for Blood."
The horrific events escalate when Mandy is abducted by Sand's disciples, including a wicked woman named Marlene, who drugs her and inflicts a horrifying sting upon her: "The Cherry on Top." When Sand confronts Mandy, he reveals his delusions of grandeur as a failed musician turned cult leader, exposing himself in a fit of madness. His reaction to her laughter is one of rage, igniting a violent chain of events that has tragic repercussions.
Sand captures Red, tying him with barbed wire and showcasing his attempt to force Lucy into an act of desperation that proves fruitless. Red's anguish reaches a peak when he witnesses Mandy being tormented, her life cruelly taken in front of him. Overcome with grief and rage, Red breaks free, and amidst the chaos, he mourns her ashes, his heart filled with fury for those responsible.
In an emotional breakdown, Red discovers a surreal advertisement for "Cheddar Goblin." Awakened by nightmarish visions, he learns from his friend that the deformed biker group is called the "Black Skulls," twisted by a traumatic experience with LSD. This revelation propels him to forge a weapon of vengeance, an ax, and to set off on a relentless pursuit of the biker gang.
As the title Mandy unfurls across the screen, Red embarks on a bloody journey, taking down bikers with deadly precision and discovering the depths of his own rage and despair. After awakening in the lair of the Black Skulls, Red fights tooth and nail to survive, embracing the violence surrounding him. The bloodshed does not faze him; instead, he revels in it, becoming a harbinger of wrath against those who wronged him.
His path leads him to the Chemist, the creator of the wretched LSD, who guides Red toward Sand's hideout. After a series of grueling confrontations, Red brutally dispatches the remaining bikers and confronts Sand in his twisted sanctuary. This showdown culminates in a grotesque display of power as Red proclaims, "I'm your God now!" before crushing Sand's head in a final act of vengeance.
Fleeing from the chaos, Red envisions Mandy's serene presence beside him as he drives away, but the disturbing reality reveals a figure irrevocably altered by his dark journey and the drug's influence. As credits roll against a stark black background, the silence encapsulates the madness of Red's quest, leaving audiences with an unsettling sense of both resolution and horror.
