In the opening scene, Cassie Sullivan, portrayed by Chloe Grace Moretz, is seen wandering through a desolate forest, clutching a gun. She stumbles upon an abandoned store and scavenges for any available supplies. Suddenly, a voice calls out for help, and Cassie discovers a man hiding at the back. Tension escalates as both point their guns at each other. The man lowers his weapon, but Cassie remains steadfast. Demanding he reveal what he is hiding, she is startled when a light flashes from his hand, leading her to shoot him. The horrifying realization strikes when she sees he was holding a crucifix.
Flashback to several months prior... Cassie was no different from many typical 15-year-olds, navigating high school life in a suburb of Cleveland, Ohio. She lived with her parents, Oliver (Ron Livingston) and Lisa (Maggie Siff), along with her younger brother, Sam (Zackary Arthur). With a best friend named Lizbeth (Gabriela Lopez) and a crush on football player Ben Parish (Nick Robinson), her life seemed ordinary. But when mysterious alien spacecraft appeared in the sky, everything turned upside down as the visitors, dubbed “The Others,” hovered menacingly above.
The first wave struck—the electromagnetic pulse shut down power globally, causing planes to plummet and resulting in a catastrophic death toll. With no fresh water supply, Cassie and Sam found themselves dredging water from nearby lakes. The second wave unleashed ferocious earthquakes and overwhelming tsunamis, leading to more devastation. The third wave introduced a manipulated strain of avian flu, claiming lives including those of Lizbeth and even their mother, Lisa. In a moment of grief, Cassie, Sam, and Oliver buried Lisa in their front yard and grieved their loss.
As events unfolded, they transitioned to a survivor camp. In due time, a dust cloud heralded the arrival of military personnel led by Colonel Vosch (Liev Schreiber), who claimed to offer assistance. The adults were alarmed as he delivered the news of a fourth wave, threatening human lives as The Others began utilizing humans as hosts. Chaos ensued, resulting in the deaths of nearly every adult, including Oliver. Heartbroken, Cassie resolved to navigate her perilous path alone.
At Camp Haven, the military training facility, Cassie found Ben and Sam among other recruits, where Ben was nicknamed "Zombie" and Sam "Nugget." Under the watchful eye of Sergeant Reznik (Maria Bello), Ben faced a moral dilemma when given a chance to kill a suspected Other, spurred by his grief.
As Cassie made her way back to the convenience store from the opening scene, she attempted to make sense of her actions. Even as she navigated an abandoned freeway strewn with the remains of the fallen, danger lurked. A sudden gunshot hit her leg, and as chaos spilled over, Cassie crawled towards safety but ultimately succumbed to unconsciousness from blood loss.
Meanwhile, Ben continued his grueling training and formed a bond with fellow recruit Dumbo (Tony Revolori), and they encountered the formidable Ringer (Maika Monroe), an exceptional marksman who taught the boys critical shooting techniques.
Cassie awakened, cared for by Evan Walker (Alex Roe), who tended to her wounds. Though she longed to reunite with Sam, Evan warned her of the dangers outside. With instincts honed, she attempted to escape, only to trigger one of Evan’s traps. As they grappled with their looming danger, a new connection sparked between them.
Within Camp Haven, Colonel Vosch informed Ben that the fifth wave had commenced. Gifted with a special helmet to detect Others, Ben prepared to re-enter this treacherous world. As he and the recruits set out to confront potential threats, they discovered the horrifying truth: the children themselves were the weapons in this war, manipulated by the military.
Cassie learned that Evan was not entirely human after he killed another person in the woods, revealing that his transformation tied to the alien invasion. Despite his declaration of love, she recoiled, ultimately joining forces with the military against the looming danger.
At Camp Haven, tragedy struck as Cassie faced off with Reznik, exposing the military's true intentions and their status as Others. Amidst the chaos, Ben confronted Vosch, who confirmed the dire reality that they were the adversaries. The facility was ultimately breached, leading to a narrow escape as Cassie triumphed and reconnected with Sam.
As they fled, a bitter farewell was shared between Cassie and Evan, with the facility erupting in flames behind them. Rescued by Ringer, they set up a new camp amidst the destruction, united with their fellow survivors. Cassie concluded her tale with a message of resilience—hope may flicker, but it remains the powerful force driving their survival.
