Sheriff's deputy Rick Grimes is shot and wounded in an altercation with criminals. He awakens from a months-long coma in an abandoned and badly-damaged hospital. Rick leaves the hospital and discovers an apocalyptic world overrun with zombies, colloquially called "walkers" and "biters". He returns to his house to find his wife and son missing, then meets survivors Morgan Jones and Morgan's son Duane, who initially mistrust Rick but take him in and explain the situation. Morgan arms Rick who then travels to Atlanta, Georgia, wherein the Centers for Disease Control and Prevention (CDC) is said to have set up a quarantined Safe Zone within the city. Instead, he discovers that the city has been overrun by walkers and soon finds himself surrounded by them. After being rescued by Glenn Rhee, Rick meets part of Glenn's group hiding in a nearby department store, including Andrea, T-Dog, Morales and Jacqui. Walkers overrun the store, forcing the group to leave behind Merle Dixon, an unstable and violent member of the group whom Rick had handcuffed to a drain pipe on the roof.
A few miles outside Atlanta, Rick's wife Lori and son Carl have been surviving at a camp with Shane Walsh, Rick's police partner and best friend. Other people at the camp include Andrea's younger sister Amy, Dale Horvath, who's RV is at the heart of the camp, Carol Peletier, her abusive husband Ed and preteen daughter Sophia, and mechanic Jim. Rick does not know that his family is part of the other half of Glenn's group. Shane unintentionally misleads Lori into believing that Rick is dead, as he himself believes. Thinking herself a widow, Lori begins an affair with Shane.
Rick reunites with his family and the rest of the group at the camp and begins sharing the command with Shane. Upon discovering that Rick is alive, Lori immediately ends her affair with Shane. Rick decides to return to Atlanta with Glenn, T-Dog, and Merle's younger brother Daryl, to rescue Merle and collect a cache of guns Rick had left behind. They discover that Merle had fled after sawing off his hand. They arrive back at the camp to find it under attack by walkers. Several group members are killed, including Ed and Amy. Jim is later revealed to have been bitten. The group decides to travel to the CDC headquarters in Atlanta in hopes of finding answers and a possible cure for Jim. Mid-journey, Jim asks to be left on the side of the road to die.
At the CDC, only one staff member, Dr. Edwin Jenner, remains. He is the widower of the former CDC director (the "Einstein of her field") whom he was forced to fatally shoot after she was bitten by a walker. He shows the video of her hours-long demise and eventual killing to the adults in the group to help explain the disease and its progression. All other CDC personnel have either fled or committed suicide. Jenner explains that he continued researching the pandemic only to fulfill a promise to his wife as he believes the outbreak is the human "extinction event". He believes that the disease is caused by a microorganism – such as a virus, bacterium, fungus, or parasite – or possibly even by Divine Intervention.
Jenner concedes that he has been unable to find a cure, but adds that researchers at France's version of the CDC may have been about to discover one before their generators ran out of fuel, causing that facility to automatically self-destruct as it had been designed to do under such circumstances to prevent the escape of deadly pathogens. Lack of fuel for the Atlanta CDC's own emergency generators soon initiates building safety protocols also designed to destroy that facility and all of its occupants. Jenner and Jacqui decide to remain inside. Andrea initially decides to remain behind, but Dale coaxes her to leave under threat of him remaining, too. Before Rick and the others escape, Jenner whispers something into Rick's ear which causes his face to register a look of shock. The remaining survivors escape just before an explosion incinerates the CDC building, killing Jenner and Jacqui.
Season 2 (2011–12)
Main article: The Walking Dead (season 2)
The second season begins with Rick and his group of survivors escaping the CDC. They choose Fort Benning as their next destination. Along the way, they encounter a traffic jam of abandoned vehicles on Interstate 85. The group loots several vehicles, and assumes that all is well until a large herd of walkers approaches and are forced to disperse and hide under cars. A walker chases Sophia out from her hiding spot and, with another walker, pursues her into the woods. Rick finds her but loses her again after drawing off the walkers. During the group's search for Sophia, hunter Otis accidentally shoots Carl. To get medical help for him, Otis leads Rick and Shane to a large, isolated farm owned by veterinarian Hershel Greene, then helps Shane look for medical supplies at the local high school. After finding the supplies, Shane injures his leg and leaves Otis for the walkers so that he can get away. The survivors then move to the farm while Carl recovers, trying to co-exist with Hershel's family, but dangerous secrets and disagreements over leadership cause tensions to rise. Lori is revealed to be pregnant (she is unsure whether Rick or Shane is the father), and Glenn builds a romantic relationship with Maggie, Hershel's elder daughter. Dale and later Rick confront Shane about his selfish actions, including his responsibility for Otis' death. Glenn also discovers then reveals that the barn is full of walkers, some of whom are Hershel's family members and neighbors. An angry Shane releases the walkers, all of whom are quickly exterminated, including Sophia who is reluctantly shot by Rick.
Beth, Hershel's youngest daughter, collapses in shock over the barn incident, which included her face-to-face encounter on the ground with her mother-turned-walker who tried to bite her. Hershel disappears to grieve for his wife and other zombie family and friends killed outside the barn. Rick and Glenn find him drinking at a local tavern, then try to coax him to return to the farm. At the tavern, they meet two other survivors (Dave and Tony). The situation rapidly turns sour, so Rick is forced to kill the two men in a gunfight. The dead men's group quickly finds and opens fire on Rick, Hershel, and Glenn at the bar. The noise attracts a large herd of walkers, forcing all involved to try to flee, but one of the attackers, Randall Culver, is injured and left behind. Rick and his group members take him back to the farm, then realize that he is likely to reveal the farm's location to his own group. As Rick and the others deliberate about what to do with Randall, a walker bites Dale, forcing Daryl to euthanize him. The group later conducts a search for Randall, whom Shane had secretly released and murdered in the woods. Daryl and Glenn find Randall — as a walker — and kill him. Daryl concludes that Randall died from a broken neck (rather than a walker's bite or scratch) and subsequently reanimated.
Meanwhile, Shane and Rick confront each other — the former having planned the fake search so he could try to murder Rick. Rick gets the upper hand and stabs Shane in the torso, killing him. Carl arrives just in time to see Shane reanimate as a walker and shoots him down. The gunshot attracts a large herd of other walkers, who quickly overrun the property. In the ensuing battle and escape, Beth's boyfriend Jimmy and Otis's wife Patricia are devoured, and Andrea is left behind. Andrea survives on her own and is later rescued by a hooded woman carrying a katana sword and accompanied by two chained, armless, jawless walkers. The remaining survivors regroup but are forced to make camp when their vehicles run low on gasoline. Lori at first shuns Rick after learning that he had killed Shane. After hearing of Randall's fate, Rick finally reveals what Jenner had whispered to him at the CDC: every survivor is infected with the walker pathogen and will thus reanimate after death regardless of its cause. Rick also discloses to the rest of the group that he was forced to kill Shane in self-defense. Later that night, the group questions Rick's leadership, but Rick asserts a dictatorship-style ultimatum and solidifies his command of the group. In the final scene, a large prison is shown looming in a pan out.