A hook differs from a thesis statement. You have shared your thesis statement, which will structure your paragraph or essay and which is an arguable statement you can defend using evidence. A hook has a different purpose: it is what you use to catch the readers' interest or raise their curiosity. It is almost always the first sentence or sentences of an essay or paragraph, because, as Zinsser points out in his classic On Writing Well, as does Trimble in Writing with Style, if the first sentence doesn't grab readers, they are unlikely to move on to read the second.

Some examples of hooks in Zinsser include opening with a question, opening with an unusual fact or statistic, opening with a short anecdote, opening with a quote, or opening with description that sets a scene. Trimble adds to this opening with a gripping sentence of no more than five words.

Some ideas that work with a thesis that discusses the unfairness of racial inequality might be to ask a question that appeals directly to the reader's self interest, such as "What if you moved to a town where, because you weren't related to the main families, any lie they told about you was accepted as truth and they used this power to force you to pay heavy, unjust fines?" This makes racism relatable to any reader. Or you could do a little research about the 1930s and open with a startling fact, such as that "X number of Black men got the death penalty in the South unjustly between 1930 and 1940" to show the context. The key point is to open in a lively, interesting way.

A hook is something that grabs the attention of the reader and keeps them engaged in the writing. So it's basically an interesting way to start an essay or paragraph. It's often the very first sentence in the paragraph. It should be so interesting that the reader will want to continue reading what you have written.

This theme, "social inequality based solely on race affects people who don't deserve it," is clearly about the racism of some of the characters in the novel To Kill A Mockingbird. The charges and aggressiveness towards the black man Tom Robinson are due to the racist attitudes and world views of the other characters. 

I think what the theme is referring to is how Atticus's family is treated badly by the other white residents of Maycomb for supporting and trying to defend Tom Robinson. The white residents don't understand how a white lawyer can possibly defend a black man because they judge people based on the color of their skin and their race. So they attack the white lawyer along with Tom.

The theme actually doesn't make too much sense because all social inequality is bad and no one deserves to be a victim of racism. But this novel is a good way to understand how racism can cloud people's thinking and cause them to jump to the wrong conclusion about others simply because of how they look or what race they belong to. As the popular saying goes, "never judge a book by its cover."

As for the hook, you must make a compelling argument about the negative effects of racism. An example may be: "Racism causes people to treat others wrongly." "When people do not accept that others are equal to them, even those who have not done anything wrong may be punished." But be original and put your thoughts in your own words.

Think about how you would feel if others put you down because of your appearance. Think about how you would feel if someone made up a lie about you and attacked you just because of what you look like. Think about how it would feel to not be able to prove your innocence.

Also, consider watching a film on To Kill A Mockingbird, which may be available at your local library. It will help you better understand the story and the characters.

As part of the introduction to an essay, the writer will want to create a "motivator" that will induce the reader to become interested in the subject matter of this essay.  This motivator, or "hook" as it is also called, can be a question or a reflection by the writer; also, it can be a quotation that is relevant to the topic of the essay.

So, regarding the theme of social inequality based upon race, the characters of Tom Robinson and Calpurnia and, perhaps, even Raymond Dolphus can be examined.  With respect to these characters, those who express prejudicial statements about these persons feel a sense of social elevation above them. That is, by lowering others, they somehow feel that they have elevated themselves.  Specifically, the reader notices that Bob Ewell does this by vilifying Tom Robinson as a n---.

Now, regarding the "hook":  Why not begin with an observation of how people feel the need to always be better than someone else, no matter how socially low they are?  This cruel practice has been played out throughout time, and Bob Ewell, Atticus's neighbors, Mrs. Merriweather, and others are also guilty of it.