A few miles outside the city, Rick's wife Lori and his son Carl have been hiding away from the walkers with Shane Walsh, Rick's former colleague and best friend. They have established a camp with a small group of other survivors from around the country. After being rescued in Atlanta by members of the group and being reunited with Lori and Carl, Rick assumes a command position with Shane and must take responsibility not only for his wife and son but for the survival of the group as well. Part of the group goes back into Atlanta to recover a bag of weapons Rick left there (and to rescue Merle Dixon, who they had left handcuffed on a department store roof). But on their return they find that the camp had been nearly overrun by walkers. In hopes of finding medical treatment for an injured member, some of the group decides to return to Atlanta and seek aid from the CDC.
In the CDC, all but one staff member (Dr. Edwin Jenner) have fled or killed themselves. Dr. Jenner explains his research into the cause of the "zombie apocalypse". But the CDC building is not the haven the group believed it was. The next day, lack of fuel for the generators causes safety protocols to begin, which will result in the destruction of the CDC. Although they are nearly trapped in the building, Carol reveals a grenade she took from Rick's clothing, and the group is able to use it to blow out a window. Dr. Jenner explains that the French may have found a cure, as they were the only nation whose scientists stayed in their labs. Nonetheless, Dr. Jenner elects to stay in the CDC despite the impending explosion. Before the group leaves the building, Dr. Jenner whispers something unknown into Rick's ear. Andrea and Jacqui decide to stay with Jenner as they have lost hope. Dale refuses to leave Andrea behind and elects to stay as well, so Andrea reverses her decision if only to save Dale. She and Dale escape just before Jenner and Jacqui are killed by the building's self-destruction.
