The season begins with the brothers tracking down the demons released from Hell in the previous season finale.
They become allies with a demon named Ruby (Katie Cassidy), who claims to know a way to release Dean from his demonic pact—he had sold his soul to a demon and was given a year to live in exchange for Sam's resurrection—and wants to protect them from the new demonic leader Lilith.
The CW ordered 22 episodes for the season, but interference from the 2007–08 Writers Guild of America strike ultimately limited the season to 16 episodes.
Some storylines were thus postponed, which Kripke felt ultimately benefited the season by forcing the writers to focus on saving Dean.
The brothers discover the mother changeling is using a vacant house as her base.
Inside, they find a recently-replaced Ben, the other children, and the local realtor in cages.
Isaac and Tamara trail one of the demons to a bar, but discover that all the patrons are demonically possessed.
The two are restrained, and Isaac dies after being forced to drink drain cleaner.
Dean reads about a death in Cicero, Indiana, where a man was pushed onto a power saw.As Dean helps Ben deal with bullies, Sam investigates one of the accidents—a man fell off a ladder—and notices the child is behaving oddly.A mark on the mother's neck also catches his attention. He suspects that the creatures have replaced the local children, killed the fathers, and are feeding on the mothers.As Dean's deadline approaches, their efforts are further hindered by Bela Talbot (Lauren Cohan), a professional thief of occult items who is often at odds with the Winchesters.In the United States the season aired on Thursdays at pm ET on The CW television network.