The story begins when Deputy Sheriff Rick Grimes and his partner, Shane, are in a shoot-out with an escaped prisoner. Rick is shot in the chest during the incident and is put into a coma. A month later, Rick wakes up in a hospital, but, finds it abandoned. After dressing himself, he explores the hospital, finding a corpse which falls backward into the opening elevator; as well as a cafeteria door that is blocked by a piece of wood. Rick removes the wood and opens the door only to find multiple zombies inside the room. One of the zombies lunges at Rick, which causes them to fall down a set of stairs where the zombie's head becomes decapitated.

Severely confused, Rick leaves the hospital (after locking the door with his belt to stop the other zombies) and finds a bicycle. As Rick walks toward the bike he sees a zombie that has deteriorated to nothing more than bones. At this sight, Rick temporarily breaks down. Shortly after, Rick returns to his home and finds that his house had been looted and that his family, Lori and Carl are gone. Upon exiting his home, Rick is knocked unconscious by a boy with a shovel. The boy's father quickly tells him that Rick is not a zombie, and they bring him inside. Rick wakes up and has dinner with the man whose name is Morgan Jones. The boy that hit Rick in the head with a shovel is Morgan's son, Duane Jones. Morgan explains to Rick the nature of the outbreak, which started just over a month ago. Rick finds out that before the media shut down that the government told everyone to relocate to major cities. Rick decides that Lori would have taken Carl to Atlanta where her parents live. Rick, Morgan, and Duane go to the police station in order to get supplies. Rick gives Morgan and Duane some guns and a police car while changing into a police uniform and filling a bag with guns to take with him. Morgan and Duane decide to stay behind while Rick leaves in search of his family in Atlanta. The goodbye is interrupted when a zombie appears behind a fence and Rick nearly shoots it, though Morgan tells him not to waste the bullet and the two part ways. Later, Rick returns to find the severely decomposed zombie from earlier and puts it out of its misery before continuing on to Atlanta.

On his way to Atlanta, Rick's car runs out of gas and he is forced to scavenge for gasoline at a nearby home. Inside the home Rick finds the remains of a family that committed group suicide. After throwing up from the smell, Rick continues to explore the property where he finds a horse inside of a barn. Rick takes the horse as well as an hatchet as a weapon. Rick talks to the horse and starts thinking about how things were before the outbreak. He also reminisces about the day that his son Carl was born. Rick realizes that thinking about the good old times make the outbreak seem much worse.

Rick arrives in Atlanta and enters the city to find it in ruins and overrun by zombies who swarm him and knock him off his horse. As he sees his horse being eaten by zombies he begins shooting and trying to escape the zombie onslaught. He runs into an alley where he meets a supply runner named Glenn. Glenn tells Rick to stop using his gun and to follow him. Rick and Glenn exit the city safely. Glenn explains to Rick that everyone in the city died in under a week and Rick momentarily breaks down thinking that his family has been killed. Glenn then explains to Rick that there is a camp outside of the city where there are a group of survivors and that his family might be there.

When Rick and Glenn get to the camp, Rick is reunited with his wife, Lori, and his son, Carl. He is also reunited with his partner and best friend, Shane who has been protecting Rick's family since the outbreak. Then Rick is introduced to some other survivors; Allen, Dale, Jim, Carol, Sophia, Amy, Andrea, Donna, Billy, and Ben. Allen and Donna are husband and wife and Ben and Billy are their twin boys. Carol is the mother of Sophia. Amy and Andrea are sisters. Lori explains to Rick what happened during Rick's coma as well as how they set up camp when they found Atlanta impossible to enter. That night, Rick and Lori talk about everything that has happened and Rick admits to how scared he actually is.

The next day, Dale tells Rick to be careful around Shane because he thinks Shane is in love with Lori and that Shane isn't happy about Rick being back. Rick and Shane go hunting while Lori, Donna and Carol wash the laundry. Rick and Shane study a zombie eating a deer. Meanwhile, as the women go back towards the camp after finishing their laundry, they are attacked by a zombie. Dale decapitates the zombie before it bites Donna, but, they find that the head is still alive. The zombie that Rick and Shane were studying suddenly attacks them. Rick hits the zombie in the head with his axe. The two men hear a gunshot and race back to camp. Lori cries to Rick and relays story concerning the zombie attack. It is revealed that Shane does indeed love Lori when he sees Rick and Lori hugging, now jealous. Later that night Rick and Shane talk about moving the camp to a safer area. Shane argues that they aren't moving the camp because if the government starts cleaning up the outbreak, the government would start with a major city and they would be found sooner. Rick finally agrees not to move the camp, but, insists that they need to find more guns to protect themselves.

The following day, Rick asks Glenn if he could come with him to get supplies in Atlanta. One of the purposes is to obtain firearms for the group. Jim, who happens to be the sole survivor from Atlanta, tells them the location of a gun store which is five blocks from where Rick and Glenn first met. Rick has an idea. He takes Glenn to the zombie that he and Shane had studied the day before. Rick's theory is zombies don't attack each other because of the stink of death. His plan is to rub the zombie's body parts on their clothes so that they will smell like the zombies. The plan works and they are able to go deeper into the city to obtain the firearms. While exiting the city, it begins to rain which washes away the zombie stench off. This causes an attack by the zombies. A zombie bites Rick on the shoulder as they make their escape from the city. Safely outside of Atlanta, Rick checks his shoulder only to realize that the zombie hadn't bitten through his jacket. As they head back to camp with the guns, Rick tells Glenn not to tell Lori about the zombie attack. Meanwhile, Shane and Lori talk discussing Rick going into the city. Shane wants to come inside out of the rain and offers to "keep her company". Lori rebukes him and says that he needs to stop this now that Rick is back. Shane asks Lori about the night they spent together on their way to Atlanta (strongly hinting that they had sex). Lori tells Shane that night was a mistake.

Over the course of the next couple of weeks, the group have target practice with the guns that Rick and Glenn brought back from the Atlanta gun store. Andrea quickly proves that she is the best shot in the group. Rick allows Carl to practice which causes a disagreement between him and Lori. Rick, Shane and Dale later discuss Donna, who has been complaining about Andrea and Amy staying in Dale's camper, and the upcoming winter while chopping firewood. Shane yells at Rick to shut up about everything, leaving Rick speechless. While eating dinner that night Rick asks the others what their lives were like before the outbreak. Dale says that he was a retired salesman who was traveling with his wife in their RV when the outbreak came. Dale's wife died in the initial outbreak while they were at a campsite leaving Florida. After burying her, Dale came to Atlanta to find his cousins. He met Amy and Andrea stranded because their car had ran out of gas. Andrea was driving Amy back to college so that they could have some bonding time. Andrea had a job as a clerk at a law firm. Glenn was a pizza delivery boy who was swimming in debt and was nearly forced to ask his estranged parents for money when the dead started rising. Allen was a shoe salesman in a mall who was also struggling to make ends meet. Jim simply says that he was a mechanic. Finally, Carol talks about how her husband, a successful car salesman, committed suicide when he saw his parents being eaten by zombies. She also implies that he was abusive and simply convinced her to stay with him long enough to care for Sophia. Amy goes to the RV to use the bathroom when she sees a zombie which forces her to unknowingly back up into another zombie which bites her in the neck and kills her. The survivors are attacked by a group of zombies which they are able to fight off. Carol and Sophia are saved by Glenn as Andrea grieves over Amy's body, oblivious to everything. Lori is nearly killed by a zombie, but, is saved by Carl who shoots the zombie. Jim launches into a rage and attacks a zombie while yelling at it saying that it killed his family. When all the zombies are dead Andrea shoots Amy in the head in order to prevent the reanimation. It is then revealed that Jim was bitten in the arm when he killed the zombie, though he says it is just a scratch.

The next day a funeral is held for Amy. Shane, Donna, Dale and Rick all take turns eulogizing her and Jim has perhaps his biggest speech, saying that nobody deserves this kind of death, especially a nice girl like Amy. Andrea is in a depression and Jim falls desperately ill. Meanwhile, Rick, Shane and Carl go hunting and Carl tells Rick that they don't need as much food because Amy is dead and that Jim is too sick to eat. Shane yells at Rick saying it wasn't his fault. When they return, Donna informs them of Jim's request to leave him outside of Atlanta. Jim hopes that once he turns, he can reunite with the zombified members of his family. The group bring him to the outside of Atlanta to say goodbye. The following day Shane tells Rick to get ready to go hunting. Rick tells Carl to stay behind so that he and Shane can talk. Shane starts yelling at Rick and punches him. Lori then punches Shane which causes Shane to mentally snap and run off. Rick goes to follow Shane and Carl follows his father in turn. When Rick catches up to Shane, Shane starts yelling at Rick about how Shane just lost his respect and how Lori would have changed and loved him if Rick hadn't returned. Shane then points his gun at Rick and is about to shoot him when Carl shoots Shane in the neck. Shane died choking on his own blood. The book ends with Carl saying "It's not the same as killing the dead ones, daddy" and then Rick replies saying that, "It never should be, son, It never should be."