Supernatural Season 3 premiered on October 4th, 2007 and concluded on May 15th, 2008. It consisted of 16 episodes (writer's strike) beginning with the episode "The Magnificent Seven" and ending with the episode "No Rest for the Wicked".
It begins with the army of demons that had been released when one of Hell's gates was opened at the end of Season 2. The main story arc of Season 3 is trying to break Dean from the demon deal he had made in exchange for bringing Sam back to life at the end of Season 2. There are still numerous "monster of the week" episodes scattered throughout. One new happening is a demon named Ruby who appears and helps Sam throughout the season. Ruby's knife, an ancient demon-killing knife of the Kurds, is first introduced in this season. A powerful demon named Lilith is also introduced this season. It concludes with Dean's year coming to an end. He is killed by a hellhound and dragged into the pit(Hell).