The survivors head out of Atlanta but come across a highway traffic jam. Soon a pack of Walkers come stumbling through and Andrea has to kill one of them without making noise. Young Sophia is chased by two into the woods and Rick saves her by diverting their attention. Unfortunately they can't find her and a search the next day only uncovers an abandoned church. Shane tells Lori that he plans to leave and Andrea wants to go with him.
Rick carries Carl toward the house where other survivors live. Hershal the veterinarian takes them in and begins to stabilise Carl. Rick has to give blood while Shane and Otis (the shooter) head out to find surgical supplies. Back at the RV T-Dogg's wound has become infected and he suggests to Dale that they run away. Hershal's daughter brings Lori to Rick and tells the survivors how to find them.
Shane and Otis struggle to escape the Walkers inside the school. Shane jumps out of the gym window but hurts his ankle. Back at the house Lori questions whether maybe Carl would be better off dead. Glen and T-Dog arrive. T-Dog gets stitched up while Glen prays and gets to know Maggie. Shane appears just in time to provide the surgical equipment which saves Carl but he is very shaken and Otis is dead. Out on the road no one can sleep and so Darryl and Andrea go walking in the woods.
With Carl recovering Hershel expects Rick to move his people on. Rick asks him to reconsider. Dale finds a Walker trapped in a well and the group try to pull him out. Glen and Maggie go to the local pharmacy and end up having sex. Darryl is the only one fit to go searching for Sophia and he finds some potential clues. Lori takes a pregnancy test.
Hershel becomes concerned by the lack of boundaries between his people and Rick's. The search for Sophia continues in earnest. Darryl heads out alone on a horse and gets knocked out when a snake spooks his ride. He fends off a Walker attack and the doubts of his own mind to make it back to camp. However his stumbling gait means that Andrea mistakes him for a Walker and takes a shot at him. Meanwhile Shane tells Rick that they should give up on the search and focus on survival. Glen wants to have sex with Maggie again and suggests the hay barn.
Glenn tells Dale about both the Walkers in the barn and Lori's pregnancy. Dale confronts Hershel who insists that the Walkers are just sick people and that our survivors need to move on soon. Lori struggles desperately with what to do. Glenn and Maggie fetch her some morning after pills from the pharmacy and are attacked by a Walker. Shane gives everyone a shooting lesson and Andrea seems like a fast learner. They go searching for Sophia, kill a bunch of Walkers and sleep together. Dale warns Shane that he knows what kind of man he really is and Rick finds out about the pregnancy.
Glenn tells everyone about the Walkers in the Barn. Rick tries to persuade Hershel into letting them stay. Hershel shows Rick what he will have to do to Walkers if he wants to stay. Dale tries to hide the guns from Shane but fails. Darryl keeps Carol's hopes alive temporarily.
Hershel asks Rick to get his people off his land. He then disappears for a drink and Beth goes into shock. Maggie tells Glen that she loves him. Dale warns Lori about Shane. They bury the Walkers they knew and burn the rest. Hershel is disconsolate but Rick tells him they need to keep living to give their loved ones hope. Lori comes to get them but runs over a Walker and crashes the car. Meanwhile two men enter the bar, Dave and Tony, and begin asking if they can come to the farm.
Lori fights off some Walkers before Shane arrives to rescue her. He lies to get her to come back to the farm and then restates his belief that the baby is his and they are meant to be together. Hershel, Glenn and Rick have to fight their way out of the bar after Dave and Tony's friends show up looking for them. One of them, Randall, punctures his leg on a railing. They pull him free and take him back to the farm to perform surgery. Carol is patient with a petulant Darryl.
A week has passed and Shane and Rick take Randall eighteen miles from the farm to release him. Rick also warns Shane to accept that the baby is not his. They find some abandoned buildings but Randall reveals that he went to school with Maggie. They fight over what to do with him and then a group of Walkers attack them. Back at the farm Beth is speaking again but talks openly of suicide. Lori wants to stop her but Andrea suggests giving her the choice.
Randall reveals that he is with a heavily armed group of thirty men. Dale is the lone voice against the execution of Randall. Carl talks back to Carol and then takes a gun and heads off into the forest alone. He taunts a Walker that is stuck in a bog and it almost escapes. Rick tries to shoot Randall but pulls out when Carl walks into the scene. Dale is attacked by the bog Walker and Darryl is forced to end his life.
After burying Dale, Rick instructs everyone on making their preparations for winter. Carl owns up to Shane about his part in Dale's death. Shane tells Rick who offers Carl a gun. Lori says she's sorry to Shane for everything that's happened. Shane takes Randall out into the woods and kills him. He then smashes his own nose and pretends that Randall escapes. Darryl and Glenn find Walker Randall and put him down. Rick figures out what happened and kills Shane. Shane soon rises.
Having followed a helicopter from Atlanta all the way out to Hershel's farm the Walker herd now descend. Rick and Carl set fire to the barn to try and distract them. The others try to lure them away with their cars. Neither tactic works and Patricia and Jimmy are killed. Andrea is left behind and runs alone through the forest. The others meet up at the spot where they left supplies for Sophia. They head off but soon Rick's car runs out of gas. He admits to the group that Jenner told him that they are all now infected and that he killed Shane.