The season follows Sam and Dean Winchester as they deal with their father's death and continue to hunt down the yellow-eyed demon known as Azazel, who caused the fire that led to the deaths of their mother over 20 years ago and later, Sam's girlfriend, Jessica Moore. They have assistance not only from their friend Bobby, but from new allies Ellen Harvelle, her daughter Jo, and Ash. Part of Azazel's master plan is eventually revealed as he gathers Sam and others like him, leading to Sam's death. Dean makes a deal with a crossroads demon to resurrect Sam in exchange for his soul, which will be collected in one year. In a final confrontation, in which Dean kills Azazel with The Colt using the last of the original bullets, a gate is opened, releasing hundreds of demons from Hell.