In a post-apocalyptic world, a deadly plague has ravaged humanity, turning people into vampire-like creatures. Dr. Robert Morgan is the sole survivor in this desolate landscape. Immune to the virus due to an earlier bat bite, he spends his days methodically hunting and disposing of the nocturnal beings while fortifying his home against their nightly assaults. Haunted by memories, he remembers the loss of his wife and child, replaying old home videos and reminiscing about the past. His grim routine highlights his enduring loneliness as he struggles to maintain sanity amid despair.

Morgan conducts research by day, desperately seeking a cure for the plague. His meticulous collection of scientific data and execution of experiments fuels his hope to reverse the catastrophe. During his hunts, he gathers infection samples from dispatched creatures, studying them for answers. One day, he encounters a seemingly unaffected woman named Ruth and brings her to his home. Though he is skeptical, his longing for companionship draws him to her. As they bond, Morgan uncovers truths about her identity that challenge his understanding of the plague and his place in this altered world. Events unfold rapidly as Morgan faces moral dilemmas and uncovers shocking revelations that question everything he's believed about the infection and survival.