One of the easiest ways to write an argumentative essay about a long book is to choose one theme on which to focus the essay, then develop the essay by analyzing the techniques the author uses to develop the theme.  To start, pick a basic theme subject presented in the book.  An obvious and well-supported example might be the theme of betrayal.  Then, create an open-ended question that will guide your argument.  For example:

What is the author trying to say about the theme of betrayal and how does he accomplish this?

With this open-ended question, you can brainstorm a list of ideas that are backed up by evidence from the text.  Here, you would definitely want to include Rashid's betrayal (whose betrayal led to his arrest?) and the fact that he does not further betray his friends, even in the face of torture.  Suleiman is also involved in betrayal.  In one instance, he betrays a friend and feels shame.  In another, he betrays his father, and does not believe he did anything wrong.  Later in the novel, he feels betrayed by his family.

Through the examples above (and others which you will continue to list as you brainstorm), look for emerging patterns and commonalities.  Attempt to answer the original question (from above) in a general sentence which is supported by three sub-categories.   Your statement (or main argument) will become your thesis.  The three categories, into which you will group your ideas, will become the main points of your argument and therefore the outline of your essay.