After the United States detonates an experimental weapon off the eastern coast of Tasmania, the city of Hobart is destroyed and the island’s remaining residents are left fighting for survival. Some of the brain-dead victims later begin to regain motor function, turning violent as they wake. In the midst of this crisis, American physiotherapist Ava Newman volunteers to join an Australian military effort whose goal is to retrieve and dispose of the bodies left scattered across the island. She is assigned to the northern region, far from Woodbridge, where she tirelessly retrieves corpses and signals soldiers to kill any undead that rouse from their sleep.
On the road, Clay, another volunteer, teams up with Ava as they discover a motorcycle hidden in a garage. The pair make a bold, dangerous choice: abandon their unit and drive across Tasmania to search for Mitch, Ava’s husband, who was abroad on business in Woodbridge. The journey soon tests their resolve as they push into abandoned towns, empty stations, and the desolate landscapes between them. During a rest at an old petrol station, the two are ambushed by an undead creature, and their fate appears bleak until a lone soldier named Riley appears and pulls Ava to safety. Riley locks Ava in a toilet to question Clay, and Ava drifts into a sleep filled with memories of Mitch as the hours slip by.
When Ava wakes, she learns that Clay has run off. Riley offers to escort Ava to Woodbridge, but his plan shifts: he leads her to his home for a meal and a long, heavy conversation about the spouses who fell to the detonation. The two menacingly intimate moments give way to a disturbing request from Riley: Ava should wear his wife Katie’s clothes and dance with him. Ava, caught between fear and a desperate need for human connection, agrees and the two share a fraught dance and a fragile fantasy of being each other’s partners. The tension spikes when Riley discovers that Ava has not removed her wedding ring, and violence erupts. Ava escapes through a window and uncovers Katie’s pregnant undead corpse in Riley’s bed, a shrine surrounding the scene.
Riley insists that he is still alive, and Ava’s escape becomes a tense chase through the house. In the shed, she discovers many chained undead, each labeled with notes Riley has written about their behavior and unfinished business. Riley explains that those who return might be the ones with unresolved issues, and he admits that he hasn’t forgiven Ava for not wearing Katie’s ring. The confrontation ends with Ava killing Riley and driving away in his car, only to glimpse that Katie has begun to wake.
Ava makes her way to Woodbridge and rests in a camper van, taking care to bury the corpses left outside a family’s car. That night, the undead father rises from the grave and, with a shovel, digs a proper grave for himself and the other three corpses as the undead driver watches calmly, then resumes his grave-digging. Ava helps bury them and finally kills the driver with the shovel before continuing her escape.
Through a series of flashbacks, the strain on Ava and Mitch’s marriage becomes clearer: infertility had created tension, driving Ava to have an affair that Mitch discovered just before he left on his trip. Ava eventually reaches the resort where Mitch was staying, only to learn that Mitch did not wake up from death and had cheated on her with a coworker before he died. Clay later finds Ava at the hotel, and the two form a bond as they face the fallout of a world shattered by catastrophe. Clay explains that his own wife and daughter want nothing to do with him, and that joining the effort was his way of proving he’s not selfish.
After spending the night together, Ava and Mitch place Mitch’s body in a motorboat and set it on fire, sending it out to sea as a final, ember-like gesture of closure. Retracing their steps northward, they encounter Katie, who has somehow given birth. Katie turns away from Ava, Clay, and the sound of a crying baby, leaving them to follow the newborn into nearby stone ruins. To their astonishment, the infant is alive and perfectly healthy, seemingly free of the undead’s corruption. Ava cradles the baby, tears of joy glistening as she realizes a new life has somehow begun amid the ruin.
