October Novel Prep Challenge

As this is a new assignment (not on last years calendar) I need a little help. I'm not really sure how to go about describing the theme for my novel. I guess you could call what I'm writing a romantic crime drama. Oh I don't even know anymore. Check out my short premise to give you some idea what my novel will be about.
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Now can someone please explain what a theme is and how I go about describing it?
Thank you, in advance, for your help.

Be blessed and be a blessing,
Fancy