Investigating the crime, Detectives Johan Stemmy and Anthony Heron are confounded and chilled by the fact that the man Shawn killed had been dead for twelve hours at the time of the incident. Their investigation takes them to the apartment of the Koplowitz family where they
confront Mrs. Lucy Koplowitz, and her eight year old daughter Zoe, already zombies. Zoe bites Stemmy in the leg, thus infecting him. He dies hours later and Heron sees to it that he will never turn.
A week later, a customer, of Push Ups gym, Karl Rappaport, becomes ill while working out and drops a weight on his foot. Abby Benjamin wheels him to the Sisters of Charity ER and waits for a doctor to attend him. While waiting, Karl dies from the infection. The doctors bring him straight back and try to revive him but to no avail. Minutes later, he awakens on his own. A nurse comes to help him only to be bitten by the zombie that he has become. Her wound is severe and it only takes seconds for her to die. Shortly thereafter, there are two zombies in the ER. While the chief of emergency medicine tries to get everyone out, a young doctor named Peter Ventura recognizes the threat and locks down the ER.
Coincidentally, Anthony Heron is also at Sisters of Charity that day, visiting with the surgeon who is scheduled to operate on him the next day. Heron has been diagnosed with lung cancer. The situation in the emergency room draws his attention however, and he takes charge of the situation outside the locked down ER.
Before long, there are three zombies in the ER, as a security guard, attempting to subdue Karl, is himself overrun and partially eaten. The ER chief, Abby, Ventura, and three others barricade themselves inside one of the exam rooms. One of their number is bitten and they all know what her fate will be. When the zombies break through, the chief uses their bitten companion as bait and winds up trapping herself inside while the other four escape. Her success, however, effectively traps the zombies in the room and the police are able to come in and dispatch them.