Deputy Sheriff Rick Grimes wakes up in the hospital, after being shot, to find his town overrun by flesh-eating zombies. After making friends with survivor Morgan Jones and his son Duane, Rick sets out to find his wife and son.
While searching for Merle, Rick and the others come across another group of - seemingly hostile - survivors. Meanwhile, back at camp, Jim is deeply disturbed by a dream he cannot fully remember, a dream which may turn out to be prophetic.
Rick tries to make contact with Morgan to tell him his location. Back at camp, after the fight with the zombies, Jim has been bitten and is slowly beginning to change; Andrea mourns over Amy's death; and Shane blames it all on Rick for leaving. Now that camp isn't safe anymore, Rick decides that it's time for them all to move out. He plans to take them to the C.D.C., a military base, to find a cure for Jim and, hopefully, more survivors.
At the C.D.C., Rick and the others find Dr. Edwin Jenner, a scientist who is on the verge of suicide. But just when they think they're safe, Jenner tells them that the building is on a countdown to self-destruct.