This letter revived in my memory what I had before forgotten, the threat of the fiend-- "I WILL BE EITH YOU ON YOUR WEDDING-NIGHT!" Chapter 22, Page 187
How can I describe my emotions at this catastrophe, or how delineate the wretch whom with such infinite pains and care I had endeavored to form? Chapter 5, Page 61
If I do, swear to me, Walton, that he shall not escape, that you will seek him and satisfy my vengeance in his death. Chapter 24, Page 206
Shelley enjoyed the use of foreshadowing in her novel. One major event was in chapter 22, Victor is reminded of the threat that the monster made. Victor was concerned thinking about the monster being at his wedding, he believes that the monster plans on attacking him. Now he must wait and see what really happens on his wedding night.
Victor had spent a long time working on his creation, he wanted everything to be just right. He had isolated himself from his friends and the outdoors trying to make his creation come to life. During this time he kept getting sicker and sicker but believed that his accomplishments would make everything better. The Romantics believed in individualism and absorbing the natural world. For Victor, that was Frankenstein.
In chapter 24, Shelley takes us back to the scene where the novel began. Victor is on the ship with Walton after being nursed back to health. While on this trip, Victor tells Walton his story and asks Walton to continue his hunt for vengeance after he dies. The romantics tended to write about illness or exotic places because that's what they were going through. They wanted to escape reality so they did through their writing.