The 5th Wave by Rick Yancey follows 16-year-old Cassie as aliens invade Earth in five waves to wipe out humanity. Cassie survives the initial waves and fights back against the aliens who have kidnapped her younger brother Sammy. On her journey to rescue Sammy, Cassie is saved multiple times by Evan and encounters former classmates and aliens. The novel is a thrilling young adult story about humanity's struggle to survive a hostile alien invasion.