Season 2

Season 2 begins after a car crash from Season 1 has left Dean comatose. John summons a demon and trades his own life so that Dean can be saved. The season again has the two boys hunting the supernatural but the back plot is that they are searching for "The Colt", a gun that is thought to be able to kill any demon. Later in the season it is revealed that the demon that visited Sam's nursery and killed his mother, had done the same to many babies at that time and was raising an army to fight. In one episode, Sam is killed by another (Jake) that was cursed by the "yellow eyed demon". Dean goes to the crossroads to make a deal with demon there and resurrects Sam. As his part of the deal, Dean is given one year to live. Sam awakes and he and Dean search for Jake to stop him from opening the gate to hell. They arrive as he is opening the gate and Sam shoots and kills Jake after the gate has been open. The "yellow eyed demon", who is in possession of the Colt, laughs at Dean and aims to shoot him. Dean's father then comes out from the gate, stops the demon thus saving Dean again. Dean obtains the Colt, shoots and kills the "yellow eyed demon" after 100's of demons escape to the earth. John then floats up to heaven, free from the grasps of hell.

http://scifiwire.com/assets_c/2009/11/Supernatural_Colt-thumb-550x304-28755.jpg

Next up, Season 3