United Nations employee Gerry Lane traverses the world in a race against time to stop the Zombie pandemic that is toppling armies and governments, and threatening to destroy humanity itself.

       Former UN investigator Gerry Lane, his wife Karin and their two daughters are in Philadelphia when the city is attacked by zombies. Everyone bitten by a zombie quickly becomes one as well. As chaos spreads, the Lanes flee to Newark, New Jersey and take refuge in the apartment of a couple and their young son, Tommy. After zombies infiltrate the building and infect Tommy's parents, UN Deputy Secretary-General Thierry Umutoni—an old friend of Gerry's sends a helicopter that transports the Lanes and Tommy to a U.S. Navy vessel in the Atlantic Ocean, where scientists and military personnel are analyzing the worldwide outbreak. Dr. Andrew Fassbach posits that the plague is a virus, and that development of a vaccine depends on finding the origin. Gerry reluctantly agrees to accompany Fassbach to the site of the earliest known outbreak after it is made clear that he and his family will be removed from the ship if he does not.

       Gerry and Fassbach fly to Camp Humphreys, a military base in South Korea, where they are attacked by zombies. Running back into the aircraft, Fassbach slips, falls and accidentally discharges his gun, killing himself. 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 tells Gerry to go to Jerusalem and talk to someone named Jurgen Warmbrunn. The zombies are attracted to sound, so Gerry and his team quietly bike back to their aircraft. Karin phones Gerry at the wrong time, however, causing zombies to attack. Infected, Captain Speke commits suicide. Gerry and the pilot escape.

      In Jerusalem, Gerry meets Jurgen Warmbrunn, who explains that months earlier, he had taken seriously an intercepted message that Indian troops were fighting the rakshasa ("undead"). As a result, the Israelis reacted more quickly to the danger than anyone else. The city itself is enclosed by very high walls and heavily guarded. Survivors are carefully let in, but loud celebratory singing by some of them incites the zombies to climb over each other at the wall, eventually scaling it and entering the city. Jurgen orders some Israeli soldiers to escort Gerry back to his plane. On the way, Gerry notices zombies ignoring a sick old man and an emaciated boy. One of Gerry's IDF escorts, a soldier who identifies herself only by her rank, Segen (lieutenant), is bitten on the hand. Gerry quickly amputates it to stop her from turning into a zombie. Discovering that his plane had already left, Gerry and Segen escape on a commercial airliner as Jerusalem is overrun.

       Gerry has a revelation. He calls his wife and talks to Thierry. He asks Thierry to find the nearest World Health Organization facility from Israel. Gerry heads up to the cockpit and waves his phone at the camera. After taking the call, the pilot tells Gerry that they are headed to Cardiff, Wales. When a stowaway zombie is inadvertently allowed into the cabin in mid-air, Gerry uses a grenade to blow open a hole in the side of the airplane; the infected are blown out, but the plane crashes. Gerry is injured, but both he and Segen survive. They proceed to the WHO facility, where Gerry loses consciousness for three days. When he awakens, he explains to the remaining staff his theory, based on his observations: the zombies ignore the seriously injured or terminally ill, since they would be unsuitable hosts. If they can infect people with a deadly but curable disease, they would be safe. Unfortunately, the facility's pathogens are in a wing overrun by the zombies. Gerry, Segen and the lead WHO doctor quietly sneak in, but accidentally make the noise. Chased, they become separated. Segen and the doctor return to safety, while Gerry reaches the pathogen vault. A zombie arrives outside the only entrance, forcing him to inject himself. After waiting a while for the disease to take effect, he opens the door. The zombie enters the vault but, sensing his infection, does not attack. Neither do the others he encounters while returning to the main wing where he is given a cure for the disease.

       Gerry and his family, who have adopted Tommy, are reunited in a safe zone at Freeport, Nova Scotia. A "vaccine" is developed and issued to troops battling the infected, and is also parachuted to other survivors. There is hope, though Gerry admits that the war is not over.