In the vibrant city of London, an ambitious medical student named Victor Frankenstein (James McAvoy) finds himself captivated by a circus performance. During the show, he steps in to rescue Lorelei (Jessica Brown Findlay), a talented aerialist who has been injured. In the process, Victor also helps a nameless hunchback (Daniel Radcliffe), who serves as a slave to the circus' cruel ringleader and harbors a secret affection for Lorelei. Recognizing the hunchback's extensive knowledge of human anatomy, acquired from countless stolen texts, Victor decides to rescue him. After treating the cyst on the hunchback's back, which is the source of his deformity, Victor crafts a harness to enhance his posture and names him "Igor," in memory of a roommate who recently passed away.
Together, Victor and Igor embark on a groundbreaking journey to create life through artificial means. However, they attract the ire of Roderick Turpin (Andrew Scott), a zealous religious police inspector who sees their work as a violation of divine law. Igor proposes that they harness electricity to bring their creations to life, prompting Victor to gather body parts from deceased animals to construct a monstrous creature that they affectionately call "Gordon." Meanwhile, Igor rekindles his relationship with Lorelei, who is now navigating the complexities of being the mistress to a closeted baron, leading to a clandestine romance that complicates matters further.
During a demonstration of their experiment for Lorelei, chaos unfolds when Gordon escapes, causing mayhem at the university. In a frantic attempt to regain control, Victor and Igor are forced to take drastic measures. The aftermath horrifies Lorelei, who pleads with Igor to make Victor abandon his reckless pursuits. However, Igor, now aware of Victor's deep-seated guilt over the accidental death of his brother, Henry, finds it difficult to sway him. The oppressive shadow of Victor's father, Mr. Frankenstein (Charles Dance), looms over their endeavors, intensifying Victor's drive to prove himself.
As events escalate, Victor is expelled from college and is approached by Finnegan (Freddie Fox), a wealthy and arrogant classmate eager to fund Victor's ambitions for creating an artificial humanoid—dubbed "Prometheus." Despite Igor's growing resentment over his friend's fixation on Lorelei, the two partners begin their work on the imposing creation. Their bond frays when Turpin and his men storm Victor's lab to smash his experiments. In a violent confrontation, Turpin is gravely injured, and Victor and Igor are rescued by Finnegan's associates, whisking them away to his family's estate in Scotland.
Igor's suspicions about Finnegan grow stronger, resulting in a fallout with Victor. After a series of devious machinations, Finnegan captures Igor and plots to eliminate Victor once Prometheus is complete. Thrown into the River Thames with the intent of drowning, Igor miraculously escapes. He manages to find refuge with Lorelei, who takes care of him and helps him regain his strength. Once healed, Igor returns to Finnegan's estate with Lorelei to save Victor, discovering him moments away from electrifying Prometheus. Ignoring Igor’s frantic warnings, Victor activates the machine, triggering a chaotic surge that results in Finnegan's death.
In the turmoil, Turpin arrives to confront Victor about the monstrous creation, only to witness the unexpected success of the experiment when Prometheus springs to life. Victor shares a fleeting moment with his creation, but the fragile peace shatters when Turpin opens fire, leading Prometheus to retaliate. Realizing their folly, Victor and Igor unite against Prometheus, ultimately plunging a dagger into its two hearts to end the nightmare they have unwittingly created.
When the dust settles, Igor wakes to find himself once again with Lorelei, who presents him with a heartfelt letter from Victor. In it, Victor takes responsibility for all the pain caused and acknowledges that Igor was indeed his “greatest creation.” Seeking redemption and new discoveries, Victor retreats to the serene Scottish hills, leaving behind a trail of both brilliance and tragedy.
