In the heart of London, Victor Frankenstein, portrayed by James McAvoy, is a driven medical student who attends a captivating circus performance. During the show, he leaps into action to rescue an injured aerialist named Lorelei, played by Jessica Brown Findlay, with the assistance of a nameless hunchback, brought to life by Daniel Radcliffe, who is imprisoned by the circus's ruthless ringleader and secretly harbors feelings for Lorelei.
Recognizing the hunchback's extraordinary knowledge of human anatomy, acquired from illicitly obtained texts, Victor frees him from his bonds, surgically removes the cyst that distorts his back, and fashions a device to improve his posture, giving him the name "Igor" in memory of a late roommate. As they team up for Victor's ambitious pursuit of creating life artificially, they draw the ire of Roderick Turpin, portrayed by Andrew Scott, a zealous religious inspector who condemns their endeavors as heretical.
When Igor proposes the use of electricity to animate their creations, Victor scavenges body parts from deceased animals to assemble a grotesque, chimpanzee-like being they dub "Gordon." Meanwhile, Igor's relationship with Lorelei deepens as she deceives society by aligning with a closeted baron. Their affair stirs jealousy in Victor, who sees Lorelei as a major distraction. During a demonstration of their experiment, chaos erupts when Gordon escapes, leading to devastation on the university campus before Victor and Igor subdue the creature.
Horrified by the implications of Victor's experiments, Lorelei urges Igor to convince Victor to reconsider, yet Igor hesitates, understanding Victor's frantic quest stems from guilt over the death of his older brother, Henry. Victor faces expulsion from college due to his radical methods and encounters Finnegan, a wealthy peer, who entices him to create a humanoid creature. Together, they dream up an immense being known as "Prometheus," but the growing bonds between Igor and Lorelei threaten to unravel their partnership.
In a swift turn of events, Turpin and his followers storm Victor's lab with the intent to destroy his work. A violent clash ensues, resulting in Turpin losing a hand and an eye. Amidst the chaos, Finnegan's men rescue Victor and Igor, transporting them to his estate in Scotland, where he provides the financial backing needed to create Prometheus. Igor's suspicion towards Finnegan grows, and he ultimately parts ways with Victor over disagreements.
However, Finnegan reveals his sinister intentions by abducting Igor, planning to eliminate Victor once Prometheus is operational. In a harrowing moment, Igor is tossed into the River Thames to perish but miraculously escapes and reunites with Lorelei, who tends to his wounds.
Once healed, Igor returns with Lorelei to rescue Victor, only to find his friend on the brink of using lightning to bring Prometheus to life. Despite Igor’s desperate warnings, Victor activates the machine, but a power surge leads to tragedy, resulting in Finnegan's death. In the midst of the chaos, Turpin arrives, furious with Victor for the creature’s existence, only to discover that their experiment has indeed succeeded as Prometheus awakens.
Though sharing a fleeting moment of connection with Prometheus, Victor’s joy is immediately disrupted when Turpin attempts to eliminate the creature. In the ensuing battle, Prometheus retaliates and kills Turpin. Faced with the ramifications of his ambitions, Victor turns to Igor, and together they resolve to destroy the creation by plunging a knife into its two hearts.
As dawn breaks, Igor revives and is greeted by Lorelei, who presents him with a heartfelt letter from Victor. In the note, Victor expresses his remorse for the anguish he's caused and acknowledges Igor as his “greatest creation.” With a heavy heart, Victor retreats to the tranquil Scottish countryside, searching for new paths of discovery.
