If you were to write an essay about Frankenstein, what would be your first topic sentence?

Do you need a topic sentence or a thesis?  The topic sentence introduces the topic of that body paragraph.  Your thesis is, simply put, your topic + your opinion.  The thesis states what you are going to prove in the rest of your essay.  Your thesis would change depending on what you chose to write about.  You would write about the role or creator and creation, the creator's responsibility to his creation, man's alienation from society, man's desperate search for approval, revenge, Gothicism in the novel.  Those are just some possible topics.  Your thesis could incorporate one of these topics and your opinion of how the topic fits into the novel.

To easily create a topic sentence, take part of your thesis and restate it for the thesis.  For example, your thesis states, "Frankenstein intimately explores the role of creator and creation and the responsibility of the creator to that creation."  Then, your topic sentence could say, "Mary Shelley depicts the different positions the creator and creation can take."

Hope that helps!