A Twitter friend refers to the theme bubble exercise I use in The Plot Whisperer Workbook: Step-by-Step Exercises to Help You Create Compelling Stories as theme clouds, a term I prefer ever so much better. (NOTE: I wish my publisher would change all theme bubble references - never did much like bubbles anyway - in both The Plot Whisperer Workbook: Step-by-Step Exercises to Help You Create Compelling Stories and The Plot Whisperer: Secrets of Story Structure Any Writer Can Master.)
You've filled in scene clouds, perhaps all of them including the big one in the middle with your thematic significance statement or perhaps that cloud is empty as you continue to explore (experiment with ideas - use pencil).
Say your story deals with taking risks for the one you love. You introduce the concepts of both love and of risk-taking in the beginning.
Ideas for the Middle:
Use the middle as the place to deepen the reader's understanding of risk-taking and love in all the various forms you wish to portray of your theme.
Show us a character(s) who embodies the opposite -- too safe. Reveal the positive effects of caution in a relationship(s) thereby seemingly to disprove the theme. Interacting with someone who challenges his belief system creates tension in your protagonist who believes risk-taking is necessary to seize the one you desire.
Let us see what safety and caution in dating looks and feels like. Let us feel his emotion - not told about how he feels. Shown how his confusion, doubt, uncertainty shows itself through him, his actions, dialogue, attitude, posture, habits.
Characters who embody the ideal reveal a unexpected shadow-side the protagonist has failed to consider thereby seemingly to disprove the theme. Again, tension is created in scene as the protagonist's belief system is challenged.
The middle of any story is the place to deepen the readers understanding of all aspects of all plot lines through creating conflicts and challenges for your protagonist as she suffers the trickery of antagonists in their exotic world while also moving steadily, or so she hopes, toward her goal.
For tips how to plot and revise your novel, watch the free Video #1 of PlotWriMo: Revise Your Novel in a Month