Frankenstein has three separate plot lines that circulate through the novel. The first is the Robert Walton plot line that introduces and closes the novel. Walton exhibits all of the emotions that we would expect from a person hearing such a fantastic tale. This plot line is like a picture frame, in which the accompanying story line is the virtual frame that surrounds the novel's main story.
The second plot line, and most important, is the Victor Frankenstein plot line. This plot line takes up much of the novel's volume.
Perhaps the most overlooked plot line, in terms of importance, is the monster's story. Mary Shelley gives the monster a voice, and the reader can sympathize with his pain and suffering at the hands of mankind. The portion of the tale dedicated to the story of the De Lacey family is part of the monster's story.