The movie is set in a world where Earth is under attack by aliens in multiple waves, each designed to weaken and eventually eradicate humanity.
In the climax of the film, Cassie Sullivan (Chloë Grace Moretz) discovers that the aliens, known as “The Others,” have been using human hosts to blend in. She infiltrates their base to rescue her younger brother, Sammy (Zackary Arthur), who has been taken by the military to undergo training as part of a potential resistance against the aliens.
Cassie confronts the true nature of the aliens, who are planning the final wave to exterminate the remaining human population. She discovers that the fifth wave involves activating implanted devices in the surviving children, turning them into weapons against their own kind.
In the resolution, Cassie manages to free Sammy from the military facility. Together with Evan Walker (Alex Roe), a mysterious character with his own agenda, they form a plan to thwart the final wave. Cassie, Sammy, and Evan join forces with other survivors in an attempt to stop the aliens from wiping out the last remnants of humanity.
The film concludes with a setup for potential sequels, as the characters prepare for the next stage in their resistance against the alien invaders.
In summary, “The 5th Wave” ends with Cassie and her allies gearing up to fight against the aliens, setting the stage for a continuing battle to save humanity from extinction. The film combines elements of science fiction, survival, and resistance against an extraterrestrial threat.