Los Angeles is shown to be running business as usual. There are rumors circulating of an unknown pathogen inciting dangerous aggression in the infected. By the end of the second day, there are signs that the outbreak is starting to take hold within the city. In one particular incident, a man who had been in a car crash on a highway off-ramp attacks an EMT attending to him. Several California Highway Patrol officers unsuccessfully attempt to subdue the man with their batons, and are then forced to open fire. The man still does not go down until one officer shoots him in the head. The whole incident is captured on camera by news helicopters and bystanders, as well as witnessed personally by Travis and Madison.
While in hospital, Nick witnesses an elderly man go into cardiac arrest, and the subsequent insistence of the attending doctor that he be taken down to the morgue imediately, following only a brief attempt at resuscitation. This indicates that the staff are aware of the strange illness and its ability to reanimate the dead.
During the third day, Los Angeles is starting to become aware of the outbreak thanks to increased police activity as well as leaks on the internet showing the undead surviving multiple gunshots before going down. Some citizens, including police officers who are aware that something is awry, begin to leave the city, causing traffic jams on the highways.
A police-involved shooting of a homeless man in downtown Los Angeles, one of an increasing number of such incidents over the past forty-eight hours, incites a mass protest from bystanders, who are unaware that the homeless man was a zombie. As the unrest and tensions increase, the shooting of another reanimated woman at the scene causes mass panic. A full-scale riot then erupts in the downtown area, allowing infected individuals to attack and kill people without much notice. Riot police are dispatched to contain the riot, but many are also attacked by the infected amidst the chaos. As the riot spirals out of control and thousands rush to leave, the city's power grid begins to sporadically fail, causing rolling blackouts in the downtown area and outlying suburbs. This is a pattern repeated across the United States.
Riots continue to rage in the middle of the city, allowing the outbreak to spread even further. Heavily armed units of the LAPD are seen shooting undead doctors and patients at a hospital which has been overrun, the building smoldering from within and power flickering on and off. As the chaos within the city escalates and more people seek a way out, a massive blackout plunges the entire city into darkness, revealing fires in the streets and neighborhoods. Mass panic engulfs downtown LA. The next day, the California National Army Guard enters the city.
Over the next 9 days, the National Guard deploys search-and-destroy squads to root out and kill the infected, evacuate any survivors, and execute those exposed to the infected. They have also set up twelve safe zones throughout the city and suburbs. Outside the zones, many infected and uninfected corpses lay in the streets, indicating that the military is indiscriminately executing both the infected and civilians outside the safe-zones. Fires rage in the hills above the city. The civilians within the safe zones are assured that the National Guard are on the offensive, and are making good progress towards taking back the city, with rumours abounding of sactuaries further east.
Unbeknownst to the occupants of the safe zones, the situation in Los Angeles and across the country is spiraling out of control, and the military prepares to initiate "Operation Cobalt," a plan to evacuate all of its personnel from the city, humanely terminate any survivors in isolation, and bomb areas of high population to try and contain the outbreak as much as possible. A refugee center has been set up in a nearby community college, with doctors treating the wounded and National Guardsmen rounding up civilians at risk of infection. It is also revealed that the military locked up at least 2,000 infected and uninfected people in the Los Angeles Arena, dooming all the uninfected inside.
16 days after the outbreak began, Los Angeles is shown to be in ruins. Several buildings and city blocks, including iconic skyscrapers like One California Plaza and the Paul Hastings Tower, are on fire. The streets are either empty or full of infected. The highways leading out of the city are jammed up with hundreds of abandoned cars, and the city is completely devoid of any man-made light. With Operation Cobalt in effect and the last major refugee center overrun by the infected, the military officially abandons the city, leaving survivors to fend for themselves.
Los Angeles and other major cities are firebombed by the military in a desperate attempt to contain the infection. The few survivors that managed to escape LA do so on boats, casting off into the Pacific Ocean as the city is destroyed.
- While the pilot episode was filmed in Los Angeles, the rest of the season was filmed in Vancouver, Canada.
- With Los Angeles being destroyed and on fire, it is possible that most zombies and survivors who were still in the city were burned alive and killed. Which means that all characters that are zombies: Gloria, Matt Sale and Calvin were most likely "killed" by explosions.