LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
Cassie cries and says that some man killed Dr. Pam. Vosch tells some soldiers there’s been a breach, and they should secure Cassie while he takes care of it. The soldiers take Cassie to a dark room and lock her in alone. But Cassie breaks the glass of the one-way mirror with a chair and climbs out. As she tries to escape, she discovers the ventilation system.
Even after being apprehended and locked up in a room, Cassie manages to find a way to get free again and continue looking for Sammy. This shows her perseverance in the face of difficulty and how she refuses to lose hope.