Sheriff Deputy Rick Grimes gets shot in combat and awakens to a zombie apocalypse.
Police officer Rick Grimes is driving down a country road. He notices that his car is running low on gas, and stops at a station to refill. As he gets out of his car, it's revealed that many of the vehicles in the vicinity are abandoned wrecks. He fills up a gascan and heads back to his car, but stops and looks under a vehicle only to discover a child's feet. Rick stops and moves around the car, where he asks the girl if he's alright. As she turns around, it's revealed that she is undead, and is missing part of her mouth.
She growls and starts walking towards Rick, who is forced to pull out his revolver and shoot her. As she falls to the ground, he stares in shock... Several months earlier, Rick and his partner, Shane Walsh, are sitting in their patrol car eating lunch. They briefly reminisce about the past and Rick's marriage to his wife Lori. Suddenly, a dispatch comes through informing them that there are three robbers attempting to escape King County, and they are sent with other units to set-up spike strips and apprehend the robbers.
Rick, Shane and several other officers take up positions on the road and wait for the robbers, who are being pursued by another patrol car. The robbers' vehicle drives over the spike strips and flips through the air, landing at the bottom of a hill. As Rick and the other officers investigate, two of the robbers emerge from the car and begin firing wildly. They are easily taken down, and Rick turns to thank the others. Suddenly, he is shot in his side by the third and last occupant of the vehicle, who is swiftly shot down by Shane. Rick struggles to hold on while Shane runs to him and calls for an ambulance... Rick has a momentary glimpse of Shane visiting him in the hospital telling him he brought flowers from Lori, then wakes up asking for Shane. He looks around and sees that he is in an empty hospital room with no sound around him. The flowers beside him have long-since wilted, and he can't page anyone to his room. Rick painfully climbs out of bed and uses an IV stand as a crutch while he walks out of the room.
He walks into a corridor to find many dead bodies of hospital staff and army officers around him, who have all been shot in the head. After trying and failing to use a telephone, he walks down the hall and discovers a room that has been barricaded with the words "DON'T OPEN DEAD INSIDE" scrawled in spray paint on the doors. As he looks in confusion, several fingers begin trying to claw through the slit in the door. Recognizing the danger, terrified Rick heads away as fast as he can, and makes his way down a darkened stairway to an emergency exit. Outside, he finds dozens of dead and bodybagged civilians, as well as an abandoned Army helicopter. He continues walking down the street and finds a bicycle to use as a means of transportation. As he gets on, a presumably-dead corpse missing its lower half suddenly turns over and begins growling at him, and he rides away in shock. Rick gets to his family's home and goes inside, only to discover that Lori and his son, Carl, are nowhere to be found. He collapses in grief and goes outside to sit in despair, only to be hit by a boy holding a shovel. As he lays on the ground, Rick sees a man walk up and shoot one of the undead in the head, and he tries to speak to them before he goes unconscious. Rick wakes up later tied up in the home of Morgan and Duane Jones, who ask him if he's going to attack them. When he explains what happened to him and his role as a police officer, they release him and give him some food. They tell him that the world has been affected by a Zombie Apocalypse. Anyone who is dead comes back as an undead "walker", and that any bite or scratch from one will result in an infection and eventual death. Rick tells them that he thinks his family is alive, as they took all the family albums, and Morgan says they likely headed to a rumored safe zone in Atlanta. Later that night, Rick and Morgan watch as a group of walkers (including Morgan's wife, who was bit and reanimated) try futilely to get into the barricaded house.
The next morning, the three men head to the police station. They shower and Rick puts on his old police uniform, and they raid the armory for weapons. Rick takes a bagful of guns and a walkie-talkie. He gives the other to Morgan and asks him to stay in contact while he searches for his family. When Morgan and Duane leave, Rick heads back to the place he found the undead "bicycle girl" and follows a trail into the forest, where he sees her futilely pulling herself along. Rick apologizes for what happened and puts her out of her misery with a shot to the head, while Morgan goes home and tries to shoot his undead wife before breaking down in tears when he can't pull the trigger.
Rick obtains a police car and begins driving towards Atlanta, where he sends a dispatch over the police radio. In a camp outside Atlanta, a group of people (including Lori, Carl, an older man named Dale and a young woman named Amy) struggle to hear the transmission, and Amy says that she hopes the person isn't headed towards Atlanta because it's overrun. Some time later, his car runs out of gas and he stops at a farmhouse, where he finds a tame horse who has been left alone after its owners were Driven to Suicide. Rick saddles the horse and uses it to ride towards Atlanta, passing a traffic jam on the lanes leading out of the city.
Rick enters the city and rides through the streets, where he finds numerous cars that are abandoned and walkers that begin to stir after he rides past. He looks up and sees a helicopter in the distance and tries to follow it, only to run into a horde of walkers. Rick attempts to flee the horde, only to get surrounded and knocked off, losing his bag of guns in the process. Rick crawls away as the horde eats the horse. He climbs under an abandoned tank and plans to shoot himself as walkers close in around him, then sees that a hatch on the undercarriage is open and climbs in before he's bit.
Rick shuts the hatch behind him and catches his breath, only for an undead soldier to attempt to attack him. Rick shoots the soldier, which deafens him and forces him to climb out of the top of the tank to regain his hearing. He is forced to shut the hatch again when walkers climb up onto the tank.
As he thinks about what to do, a voice crackles through the radio, asking him if he's cozy...