The film begins with former UN investigator Gerry Lane, his wife Karen, and their two daughters in heavy traffic in Philadelphia when a zombie apocalypse invades the city. As chaos ensues, they head to Newark, New Jersey. UN Deputy Secretary-General Terry Umutoni, an old friend of Gerry's, sends a helicopter to take them to a US Navy ship in the Atlantic Ocean where scientists and military personnel are analyzing disease outbreaks around the world. Andrew Fassbach, a young virologist, assumes that developing a vaccine for the virus depends on finding its origin. Gerry is told that his family will be expelled unless he helps Fassbach find the source of the outbreak. Gerry and Fassbach travel with a small group of Navy SEALs to Camp Humphreys, a military base in South Korea. They are attacked by zombies, and Fassbach turns to enter the plane but slips and accidentally shoots himself. The surviving US soldiers at the camp rescue the team, and Gerry later learns that the doctor there introduced the infection to the base. A former CIA agent sends Jerry to Jerusalem, where Mossad has set up a safe zone before officially acknowledging the outbreak. The zombies attack again as the team returns to the plane, with only Jerry and his pilot escaping.
In Jerusalem, Jerry meets with Mossad chief Jürgen Warmbrunn, who explains that months earlier, the Mossad had intercepted a military transmission claiming that Indian forces were fighting Rakshasa, or "zombies." Israel has fortified Jerusalem with the help of Palestinian security, erecting massive walls around it. Loud celebratory singing from the refugees prompts the zombies to climb the walls and attack them. Jürgen orders the Israeli soldiers to escort Jerry to his plane. On the way, Jerry notices the zombies ignoring an old man and a scrawny boy. Shortly after, one of Jerry's escorts (Sigan) is bitten on the hand, and Jerry quickly amputates it to prevent infection. The two escape on a commercial jet.
Jerry radios Thierry, who directs them to a lab in Wales. Injured during a zombie attack there, Jerry and Sigan manage to reach the lab. He explains that he has seen zombies ignore critically injured or terminally ill people because they would not be effective vectors for viral replication. He suggests they test this by deliberately infecting someone. The deadly pathogen is being stored in a lab wing already overrun by zombies. Jerry, Sigan, and the WHO's lead doctor fight their way through but become separated. Jerry continues on while Sigan and the doctor return to the main building. Jerry hastily grabs vials of the pathogen, but zombies barricade the door, prompting Jerry to venture out and inject himself, testing his theory. The zombies ignore him as he returns to the main building, where his infection is identified and treated. Jerry and Sigan then reach a safe zone in Freeport, Nova Scotia. A new vaccine derived from a deadly pathogen provides camouflage for survivors to combat zombies.
