The Bride!

Frank lied to the Bride because she woke up with no memory of her past life after being revived. He took advantage of her blank slate and claimed she was his Bride who lost her memory in an accident. This allowed him to manipulate her into staying with him rather than revealing that she was actually a stranger named Ida whose corpse he had used for the experiment.

Earlier, Euphronius warns that the revived person may experience memory loss, giving Frank the opportunity to shape the Bride's reality.

Detective Wiles and Malloy connected the murders to Ronnie Reed's films after noticing that crimes occurred in cities where Reed's movies were being screened. Malloy made the connection that Frank was obsessed with the actor, so wherever Reed's films were shown, the couple would appear. This led them to Niagara Falls and eventually to a drive-in theater in Illinois.

Early on, Frank takes the Bride to see a Ronnie Reed film and later causes chaos at a screening of 'Revolt of the Zombies', establishing his obsession with the actor.

The Bride forgave Frank because despite his initial deception, she recognized that their time together had been genuine. When Frank admitted he did not know who she was before she died, she understood he had been lonely for a century and feared losing her. Their shared experiences throughout the crime spree had created a real bond that transcended the lie.

Throughout their journey, the Bride chooses to stay with Frank even after seeing him kill, demonstrating her emotional investment in their relationship.

Lupino wanted Ida killed because she possessed knowledge of his criminal activities. Mary Shelley, possessing Ida in 1936, had described Lupino's underworld operations and the identities of his henchmen Clyde and James. When Ida's corpse was revived as the Bride and became famous through the news, Lupino recognized her and realized she could expose his crimes. He executed James for failing to silence her and sent Clyde to finish the job.

The frame story establishes that Shelley inhabits Ida specifically to expose Lupino's crimes, setting up the vendetta.

The Bride decided to live as a runaway with Frank after witnessing him kill two men who harassed her outside the club. Rather than abandoning him, she chose to embrace a life on the run, showing her willingness to accept Frank's violent nature. This decision set them on their cross-country crime spree.

Frank tells the Bride to leave him after the killings, but she responds by deciding to live life as a runaway with him, indicating her own alignment with his world.

At the drive-in theater in Illinois, Detective Malloy tracked down Frank and the Bride. As they attempted to flee, Clyde arrived and fatally shot Frank in the head. The Bride escaped with Frank's body and fled to Dr. Euphronius's laboratory, with Malloy following her. This marked the violent climax where both central characters are killed.

Malloy had been promoted to lead the case and was personally invested in capturing the couple, making the drive-in confrontation inevitable.

Dr. Euphronius revived the couple after being seemingly possessed by Mary Shelley's spirit. Earlier, Shelley had explained she came to tell a story that Frankenstein never told, and she used Ida as a vessel to tell it. At the climax, with both corpses before her, Euphronius appears compelled by Shelley's narrative purpose to give the monstrous romance a twisted resurrection.

The frame story establishes Mary Shelley's driving narrative goal: to tell this specific story about the Bride, making her intervention at the end thematically necessary.

Detective Wiles recognized the Bride as Ida because he had known her before her death. He reveals that he and Ida were planning to take down Lupino together, and he feels guilt that his inaction led to her murder. At the Niagara Falls confrontation, he tells her she is really Ida, attempting to restore her true identity.

The investigation connects the crimes to Ida's past, and Wiles' personal knowledge of her provides the key to her identity reveal.

The Bride inspired a movement of female rioters who were galvanized by her rants and violent resistance against authority. During the credits, these inspired women help Wiles apprehend Lupino, ensuring the crime boss finally faces justice. The Bride's defiance became a symbol that outlived her death.

The Bride's notoriety and front-page news coverage throughout her crime spree established her as a public figure whose actions reverberated beyond her immediate story.

Mary Shelley serves as the frame narrator who explains she has a story to tell after her death that she could not tell during her life. She possesses Ida in 1936 Chicago to recount the tale of Frankenstein's monster and his Bride, using Ida as a vessel to expose Lupino's crimes while setting up the events that lead to reanimation and the monstrous romance.

The opening frame establishes Shelley as the authorial presence guiding the entire narrative, explaining why the story is being told at all.