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. While dealing with cases involving normal supernatural creatures, such as monsters and ghosts, the boys have assistance not only from their friend Bobby, who has now become their surrogate father, but also from new allies Ellen Harvelle (who has a history with John), 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. Seeing no other choice, 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 and Dean is facing the ticking clock until his contract is done.