The 5th Wave Novel by Rick Yancey

he 5th Wave is a young adult sci-fi novel by Rick Yancey, the first in a trilogy detailing a post-apocalyptic Earth after a devastating alien invasion.
The story follows 16-year-old Cassie Sullivan, who is struggling to survive four waves of alien attacks that have wiped out most of the human population. Her primary goal is to rescue her younger brother, Sammy, who has been taken to a mysterious military facility.
The narrative explores themes of trust and survival, as the remnants of humanity try to figure out who is human and who is an alien "Other" disguised as one of them.