A man and his young son struggle to survive after a global cataclysm has caused an extinction event. They scavenge for supplies and avoid roaming gangs as they travel on a road to the coast in the hope it will be warmer.
Years earlier, the man's wife gives birth to their son shortly after the catastrophe and she gradually loses hope. When the man shoots an intruder using one of three bullets they have saved for their family as a last resort, she accuses him of wasting the bullet deliberately to prevent her suicide. Removing her coat and hat, she walks into the woods, never to be seen again. The coldness of her abandonment being "her final gift", it spurs the man to take his son south in search of warmer climates.
In the present, after shooting a member of a gang of cannibals who stumbles upon them, the man is left with only one bullet. Later, exploring a mansion, he and the boy discover people locked in the basement, imprisoned as food for their captors. When the armed cannibals return, the man and his son hide. With discovery imminent, the man prepares to shoot his son, but they flee when the cannibals are distracted by the escaping captives.
Further down the road, the man and boy discover an underground shelter full of canned food and supplies. They feast and bathe. When they hear noises above, including a dog, he decides they must leave for a dog means an owner. Further down the road, the son persuades him to share food with a near-blind old man.
At the coast, the man leaves the boy to guard their possessions while he swims out to scavenge a beached ship. The boy falls asleep and their supplies are stolen. They chase down the thief and take everything from him, even his clothes. This distresses the boy, so they turn back and leave the clothes and a can of food for the thief.
As they pass through a ruined town, the man is shot in the leg with an arrow. He kills his ambusher with a flare gun he found on the ship and finds the archer's female companion in the same room. The man thinks the archer and woman were following them, but she says it was the other way around. He leaves her weeping over the body. Weakened, the man and boy abandon their cart and most of their possessions. The man's condition deteriorates and eventually he dies. The boy is approached by a man who, with his wife, two children, and dog, convinces the boy he is one of the "good guys" and takes him under his protection. The wife says they have been following the boy and his father.
Who does the man's wife give birth to ?
Their son