Patrick (Matthew Fox) is the biological father of Lu (Quinn McColgan) not Jack (Jeffery Donovan). However, Patrick was unable to deal with the death of Emma (Valeria Vereau) the woman he and Jack both loved. That, on top of the world seemingly ending, Patrick became an alcoholic. Jack takes Lu from Patrick, telling him "you are no longer her father" and raises her himself, barring Patrick from having any contact with her even though they live close by.
The zombies, once thought eradicated, have evolved to survive the conditions. After encountering a pregnant survivor, Anne (Clara Lago), she is horrified to discovered they have chained up a zombie who has been screaming out for days. Anne kills it and reveals that is how they communicate with each other. The house is swarmed with infected as they four try to survive the siege. Lu learns of survivors 50 miles away as the Jack and Patrick realize they do not have enough ammo to hold out.
Patrick, realizing they cannot all escape, tells Jack he will distract them so he, Lu, and Anne can escape to a working truck. Patrick embraces his daughter for perhaps the first time (though not telling her the truth) and goes outside to fight the infected. As the three get to the truck, Patrick is attacked nearby the fuel reserves that their houses shared. As he thinks of Emma, he throws a lit flare into the fuel and it explodes, killing him and the remaining monsters.
The film ends with Jack, Lu, and Anne escaping the area, and stopping to watch the sun rise.