Ann Burden (Margot Robbie) lives and works alone on a farm in the mountains. The surrounding rocks, her own groundwater, and special weather conditions have protected the young woman from a nuclear catastrophe of apocalyptic proportions. The town in the valley, to which she only makes short trips, is deserted and contaminated. Over time, Ann has come to terms with the possibility that she may be the last person on earth. But then, on one of her forays, she encounters engineer John Loomis (Chiwetel Ejiofor). Surprised that his Geiger counter shows no radiation here, he cockily discards his protective suit and jumps into a pond to bathe. But the surface water is contaminated and he suffers radiation poisoning. Ann takes him in and nurses him back to health. Together they make plans for long-term survival on the farm and grow closer over time. But their togetherness ends with the arrival of Caleb (Chris Pine), a young man who survived the disaster in a mine. The involuntary community of fate is increasingly put to the test when the newcomer believes he has found a soul mate in Ann, and she, in turn, finds herself increasingly torn between her loyalty to the older John and her attraction to the attractive Caleb.