The 5th Wave
The world has been devastated by four waves of alien attacks, leaving only darkness and the rule of 'trust no one.' Now, Cassie Sullivan is on the run, trying to survive the fifth wave and find her younger brother. She encounters a mysterious young man named Evan Walker who might be her only hope, but can she trust him when everyone else is an enemy?
Cassie's former high school crush, later known by the callsign "Zombie" after arriving at a military training camp; his chapters share the narration with Cassie's.
Commanding officer of the military camp where surviving children are trained to fight the alien threat.
Cassie's young brother, taken during the evacuation — finding him again is what drives her across the book.
Yes — it's the first book in Rick Yancey's The 5th Wave trilogy, followed by The Infinite Sea (2014) and The Last Star (2016).
Yes — a 2016 film adaptation starred Chloë Grace Moretz as Cassie Sullivan. No sequels were produced.