Former UN employee Gerry Lane, his wife Karin and their two daughters are in heavy Philadelphia traffic when the city is overrun by zombies that are attracted to sound. As chaos spreads, the Lanes escape to Newark, New Jersey and take refuge in an apartment, home to a couple with a young son, Tommy. UN Deputy Secretary-General Thierry Umutoni, an old friend of Gerry, sends a helicopter that extracts the Lanes and Tommy to a U.S. Navy vessel in the Atlantic Ocean where scientists and military personnel are analyzing the worldwide outbreaks. Andrew Fassbach, a young virologist, posits that the plague is a virus and that development of a vaccine depends on finding the origin. Gerry agrees to help Fassbach find the outbreak’s source after it is made clear that the Lanes will be removed from the cramped ship if he is not of use.
Gerry, Fassbach, and a small military troop fly to Camp Humphreys, a military base in South Korea, whereby they’re attacked on arrival by zombies. Turning to re-enter the aircraft, Fassbach slips, falls and accidentally shoots himself dead. After being rescued by the base’s surviving personnel, led by Captain Speke, Gerry learns that the infection was introduced to the base by its doctor, who was ultimately incinerated by a soldier with a lame leg whom the infected ignored. A former CIA operative imprisoned at the base, for selling weapons to North Korea (later found out that to help them fight the infection), tells Gerry to go to Jerusalem, where he says a safe zone has been maintained by the Israeli Mossad since before the outbreak’s official acknowledgement. As Gerry and his team return to their aircraft on bicycles, Karin—worried about her husband after he misses their pre-arranged call time—rings his satellite phone, alerting nearby zombies who kill several soldiers, with only Gerry and his pilot escaping.
In Jerusalem, Gerry meets Mossad chief Jurgen Warmbrunn, who explains that months earlier, the Mossad had intercepted an Indian military ’email’ claiming that Indian troops were fighting the rakshasa, or “zombies.” Israel had thereupon quarantined Jerusalem, erecting huge walls around it. Just as Jurgen shows Gerry that Israel is allowing survivors to take refuge in the city, loud celebratory singing from refugees prompts zombies to scale the walls and attack. Jurgen orders some Israeli soldiers to escort Gerry back to his plane. On the way, Gerry notices zombies ignoring an old man and an emaciated boy. Soon after, one of Gerry’s escorts, a soldier who identifies herself only as “Segen” (Lieutenant), is bitten in the hand, which Gerry quickly amputates to stop her from turning. Gerry and Segen escape on a commercial airliner as Jerusalem is overrun.
Gerry contacts Thierry, and the airliner is diverted to a World Health Organization (WHO) facility outside Cardiff, Wales. When a stowaway zombie attacks on approach to Cardiff airport, Gerry uses a grenade to blow the infected out of the aircraft, which also causes the plane to crash. Gerry is injured, but both he and Segen survive. They proceed to the WHO facility, where Gerry loses consciousness. He awakens 3 days later and explains to the remaining staff his theory, based on the people he’s seen the zombies ignore: the infected don’t bite the seriously injured or terminally ill since they would be unsuitable hosts for viral reproduction. He suggests that they test this by deliberately infecting somebody with a pathogen from the facility, but the pathogens are stored in a wing already overrun by zombies. Gerry, Segen and the lead WHO doctor go to get a pathogen. As they fight their way through, they get separated; Gerry continues to the pathogen vault while Segen and the doctor return to the main building. While inside the vault, after grabbing various diseases, a zombie is blocking the door, prompting Gerry to inject himself with an unknown pathogen and open the vault, thereby testing his own theory. The zombie ignores him, as do those he encounters while returning to the main building.
After being treated again by the WHO doctors Gerry, along with Segen, are reunited with his family in a Safe Zone at Freeport, Nova Scotia. Now a new “vaccine,” derived from deadly pathogens, is developed and widely issued to survivors around the world battling or taking shelter from the infected, acting as a kind of camouflage. The vaccine also helps survivors to reach quarantine zones. Many people take up offensives against the zombies, and hope is soon restored.