Early in the 20th century, Dr. Frederick Frankenstein, a respected physician at an American medical school, finds himself engaged to the glamorous socialite, Elizabeth. He often becomes annoyed when people mention his infamous grandfather, Victor Frankenstein, the notorious mad scientist he desperately wants to distance himself from. Frederick insists that his last name is pronounced “Fronkensteen”, making his irritation clear. However, when a solicitor informs him about his inheritance of the family estate in Transylvania following the death of his great-grandfather, Baron Beaufort von Frankenstein, Frederick decides to make the journey to Europe to evaluate his newfound property.
Upon arrival at the Transylvania train station, Frederick encounters a peculiar duo: a hunchbacked servant named Igor with a strange fascination regarding the pronunciation of names, asserting that his name is pronounced “Eyegor” instead of the classic “Eegor,” and a lovely young assistant named Inga. Once at the estate, Frederick meets the daunting housekeeper, Frau Blücher, who aids him in uncovering a secret passage to his grandfather's laboratory. Fueled by curiosity, he begins perusing Victor's journals, leading him to the decision to revive his grandfather's work—to reanimate the dead.
Together with Igor, Frederick embarks on a daring escapade, stealing the body of a recently executed criminal. Determined to experiment with it, he instructs Igor to procure the brain of a noted "scientist and saint," Hans Delbrück. In a comical turn of events, Igor accidentally damages Delbrück's brain in a panic and instead brings back an "abnormal" brain. Unbeknownst to him, Frederick believes he has successfully transplanted Delbrück's brain into the corpse.
Through a series of electrical charges during a terrifying lightning storm, Frederick manages to bring the Monster to life. Though it takes its initial steps, the creature, startled by a match struck by Igor, becomes aggressive and nearly attempts to strangle Frederick before being sedated. Meanwhile, the townsfolk grow increasingly uneasy about Frederick's resurrection of his grandfather's legacy. The bumbling Inspector Kemp, a one-eyed police inspector with a thick German accent, raises concerns and insists on visiting Frederick for assurances that no further creations will take place.
Returning to his laboratory, Frederick is surprised to find Blücher granting the Monster its freedom. She reveals the creature’s fondness for violin music and her own history with Frederick's grandfather. As sparks fly from a switch, the Monster escapes into the darkness. Throughout his journey, it encounters both a young girl and a blind hermit, only to be recaptured by Frederick, who enters a delicate negotiation to calm the Monster's rage through flattery and reassurance, ultimately embracing his roots as a Frankenstein.
In a dazzling public showcase at a theater filled with high-profile guests, Frederick presents "The Creature," displaying its ability to follow simple commands. Dressed to the nines in top hats and tuxedos, they perform the song “Puttin’ On the Ritz.” However, the performance is abruptly disturbed when a stage light explodes, sending the Monster into a frenzy, resulting in chaos as it charges into the audience, leading to its capture. Back in the lab, Inga attempts to bring comfort to Frederick, leading to an intimate encounter on the suspended reanimation table.
Later that evening, the Monster breaks free from prison just as Elizabeth arrives unexpectedly. In an outrageous twist, the Monster abducts her, and in a surreal yet humorous turn of events, Elizabeth finds herself oddly drawn to the creature, captivated by his unexpected charms. Meanwhile, as the townsfolk seek the Monster, Frederick uses his violin to lure it back, successfully bringing it to the castle once more.
As a mob led by Kemp storms the laboratory, Frederick ingeniously manages to transfer some of his intellect to the Monster, enabling it to calm the villagers. In an unexpected moment of hospitality, Kemp invites the aghast mob for some sponge cake and wine while diverting to a lumber mill for a light-hearted excursion.
Eventually, time passes, and Frederick and Inga tie the knot. In a uniquely whimsical union, Elizabeth now sports a new hairstyle and marries the reformed and sophisticated Monster. While Frederick and Inga enjoy a moment of marital bliss, a curious question lingers about the nature of the transfer process. Frederick's playful grunt evokes laughter as they share a delightful moment reminiscent of the Monster's own quirks. Inga, conjuring memories of her escapade with the creature, begins to serenade with “Ah, Sweet Mystery of Life,” as Igor provides a lively soundtrack atop the castle.
