A five-paragraph essay is a fairly standard writing assignment for school, but based on the wording of the question, I don't believe that the prompt is looking for a five-paragraph book summary. Generally speaking, if a teacher asks for a thesis statement, he or she is asking for the paper to make an argument of some kind. The thesis statement is more often than not contained in the first paragraph and the following three paragraphs are all started with topic sentences that support the thesis statement. The final paragraph is then a conclusion paragraph that summarizes the information just presented to readers and pushes the reader toward caring about the argument made by the thesis.
The requested hook is a way to grab a reader's attention. It should be the first sentence written down, and it has to pull your readers into the paper right away. If the reader is bored with your first sentence, that reader isn't likely to finish your paper. A quick and easy hook is asking the reader a question. "Is it possible to live on in multiple pieces?" Another good hook is to use a quote. Unwind has some really solid quotes about retroactive abortion in the early parts of the book that could work quite well.
Once the hook is set, then the next step is to come up with an argument that you would like to make about the book. This is the thesis statement. It needs to be an argument that the paper intends to prove, and the following paragraphs then provide evidence to support the argument. For example: "While an Unwind's tissues do continue to support the health of a living person, in no way does an Unwind actually go on living once the procedure is complete." For support of that particular thesis, I would focus on the chapter that narrates Roland's unwinding and his eventual and permanent lack of consciousness.