While the flu epidemic reaches deadly proportions, Rick, Maggie, and Carl are in a race against time when the Walkers start pushing against the fenced walls.
As the situation grows worse in the prison, Dr. Caleb Subramanian warns Hershel that the situation is getting dangerous. Eventually Dr. Caleb is proven right when the infected survivors die and turn into walkers. As walkers start walking out of their cells, Glenn's symptoms begin to get worse. Maggie, who begins hearing gunshots in the prison, runs into the ward to help her father. With her help, Hershel is able to wrestle a respirator from a walker in order to save Glenn. Daryl and the others return from their run with the medicine. The medicine is applied to the remaining survivors and the situation is resolved. During the incident, Hershel had to put down Dr. Caleb after he died from the illness. Now Hershel mourns for his fellow medical colleague.
Meanwhile, Rick had returned from his run. As Maggie helps her father with the situation. Rick is faced with another situation. Walkers, who have been pushing on the fences, have gathered in greater numbers are threaten to breach the prison's walls. Needing help, Rick calls for his son. They try to reinforce the fences with wooden poles. However, the walker horde is able to overcome the reinforcements. Rick and Carl fall back to get the assault rifles. Together, the father and son mow down the walkers until the threat is no more. At the end of the episode, the camera zooms out as the Governor stares with malice at the prison.