The destruction of a large Earth-bound
asteroid releases unknown chemicals. As a result,
cold-blooded animals on Earth mutate into large monsters and kill off most of humanity. During the evacuation of
Fairfield, Joel Dawson is separated from his girlfriend Aimee but promises to find her. However, a giant monster attacks their car, killing his parents. Seven years later, Joel is part of a small survivor group living in an underground bunker. While the rest of the group fight monsters and seek supplies, Joel, who freezes up in dangerous situations, is relegated to kitchen and base maintenance duties. After a giant ant breaches his colony, killing one of the survivors, Joel decides to set off on a quest to reunite with Aimee, so that he doesn't end up alone. The rest of the group support his decision, handing him a map, equipment and supplies. Passing through the suburbs, Joel is attacked by a giant
toad but is saved by a stray dog named "Boy." The dog follows Joel on his journey, warning him against poisonous berries and other dangers. Joel falls into a nest of
worm monsters called "sand gobblers", when two survivors, Clyde Dutton and Minnow, rescue him. They are heading north to the mountains, where fewer monsters live due to the colder weather and higher elevation. They teach Joel some basic survival skills, and that not all monsters are hostile. They invite Joel to join them, but he insists on continuing his journey to find Aimee. As they part ways, Clyde gives Joel a grenade. Continuing west, Boy becomes trapped by a giant
centipede monster. Joel freezes, but eventually saves Boy with his crossbow. Sheltering in an abandoned motel, they meet a robot named Mav1s. Before her battery dies, Mav1s powers his radio long enough for him to briefly contact Aimee. She tells him that other survivors have reached her colony, promising to lead them to safety. The next day Joel and Boy are attacked by a queen sand gobbler. They hide, but Boy barks, giving away their position. Joel kills the queen with the grenade, and yells at Boy for putting them in danger, causing Boy to run away. After swimming across a pond, Joel is covered in venomous
leeches and hallucinates, but is rescued before he collapses. Joel wakes to finally see Aimee. She leads a beach colony of elderly survivors who depend on her. He is introduced to the survivors, as well as Brooks "Cap" Wilkinson, a ship captain, and his crew, who had all recently arrived on a large yacht. As everyone celebrates their imminent departure, Aimee confesses to Joel that she is glad to see him, but that she has become a different person and is still mourning someone she was in love with. Crestfallen, Joel decides to return to his old base. He contacts his group on the radio and learns that it has become unsafe there, and that they too must leave. Cap sends Joel some berries to eat, which he recognizes as poisonous. Realizing Cap is not to be trusted, he rushes to warn Aimee but is knocked unconscious. Joel, Aimee, and the rest of her colony awaken tied up on the beach. Cap reveals that his group are pirates that will raid the colony, and that their yacht is towed by a
crab monster controlled with an electrified chain. Cap sets the crab to feed on the colonists, but Joel and Aimee escape and are able to fight for their lives, and Boy returns to help. After a lengthy battle, Joel has the opportunity to shoot the crab, but he realizes it is not hostile. Joel instead severs the electrified chain, freeing the crab. The creature leaves Joel and the others unharmed and instead sinks the yacht, devouring Cap and his crew. Joel recommends to Aimee that she and her colony head north. They share a goodbye kiss, and Aimee promises she will find him. Joel treks all the way back to his colony, and they too decide to head to the mountains. On the radio, Joel inspires other colonies to take to the surface. As the colonies head north, Clyde and Minnow, already in the mountains, wonder if Joel will survive the next journey. == Cast ==