Mary Shelley's Frankenstein tells the story of Victor Frankenstein, a doctor and scientist who pieces together body parts to create a monster that he reanimates. Victor is horrified by what he's created and first attempts to distance himself from his creature by drastically changing his area of study.

Eventually, Victor meets with his monster and learns that the monster is lonely and desires a mate. Victor strikes a deal with his monster—if Victor will bring him a mate, the monster and his mate will move far away from all humans. Victor hopes this will keep both people and his reputation safe.

If you consent, neither you nor any other human being shall ever see us again; I will go to the vast wilds of South America.

After considering the implications of making another monster, Victor realizes he can't possibly do so near his family and colleagues. Victor wants to avoid the monster's discovery, of course, but also knows that the way he reacts to reanimation—with an out-of-body excitement—would give him away.

I was aware also that I should often lose all self-command, all capacity of hiding the harrowing sensations that would possess me during the progress of my unearthly occupation.

Furthermore, Victor needs to convene with those philosophers who might offer insight into his undertaking and believes that by being nearby rather than corresponding via mail, he will receive quick and important assistance.

I remembered also the necessity imposed upon me of either journeying to England or entering into a long correspondence with those philosophers of that country whose knowledge and discoveries were of indispensable use to me in my present undertaking. The latter method of obtaining the desired intelligence was dilatory and unsatisfactory . . .

He decides to travel to England where he can create the monster in peace and separate from anyone who knows him.

I knew that a thousand fearful accidents might occur, the slightest of which would disclose a tale to thrill all connected with me with horror . . . I must absent myself from all I loved while thus employed.

In Mary Shelley's Frankenstein, Victor decides (in chapter 18 of the eText provided by eNotes) that his must return to England. Prior to this decision, Victor has met with his creature. After hearing the tale of the creature, Victor hears what the creature wants from him: the creature desires a mate. Victor only agrees to create the mate if the creature promises to leave all lands inhabited my mankind. Based upon this agreement, Victor agrees.

After returning home, Victor realizes that he cannot create the mate for the creature in Geneva. Instead, Victor realizes that his work needs to be completed far from his home and family (given his fears that his family may be harmed and that people will come to know that he is responsible for the creation of the creatures).

Victor, contemplating this voyage, states the following:

I had heard of some discoveries having been made by an English philosopher, the knowledge of which was material to my success.

I had an insurmountable aversion to the idea of engaging myself in my loathsome task in my father's house, while in habits of familiar intercourse with those I loved. I knew that a thousand fearful accidents might occur, the slightest of which would disclose a tale to thrill all connected with me with horror. I was aware also that I should often lose all self-command, all capacity of hiding the harrowing sensations that would possess me during the progress of my unearthly occupation.

Therefore, it is in chapter eighteen where Victor details why he must go to England to create the mate for the creature. Essentially, Victor wishes to go to England in order to keep all he loves safe, people from correlating the creature with Victor, and from his family seeing how his own mental and physical attribute deteriorate.

In Frankenstein, why does Victor want to return home?

There are a few times, mentioned in Mary Shelley's novel Frankenstein, where Victor speaks of his desire to return home.

-First, after he has created the monster, Victor receives a letter from his father. His father is asking him to return to Geneva in order to do a few things.

-"Come, dearest Victor, you alone can console Elizabeth." Victor's father wishes Victor to return home so that he can console Elizabeth given her extreme depression (because of William's death and Justine's charge with the murder).

- Victor wishes to find the creature given he knows it is responsible for William's death.

-Victor wishes to return home so that he can help Justine's case (so she is not found guilty of William's murder).

-Another reason, which appears later in the novel, Victor wishes to return home is that he is worried that the Creature will go after his family since his (Victor's) destruction of the Creature's mate. The Creature, after watching Victor destroy his mate, warns Victor that he will be with him on his wedding night. Victor knows that the Creature's warning is a promise to come after him and his bride.

-Lastly, Victor wishes to return home in order to marry Elizabeth. He has destroyed the Creature's mate and, refusing to ever create another, desires to return home in order to insure his parents' wishes come true.