Supernatural: Metamorphosis

Dean is so not happy when he finds out what Sam and Ruby have been up to - forcibly exorcising demons with the power of Sam's mind - but before the argument between the two can escalate too far, the brothers get a call from a fellow hunter about a flesh-eating creature called a "rugaru".

The Winchester boys are directed towards a normal, suburban town when Jack Montgomery (Dameon Clarke) is living an ordinary life with his wife, Michelle (Warehouse 13's Joanne Kelly) - except for the fact that Jack has developed an insatiable appetite all of a sudden and just keeps eating.

Soon Jack's eating raw meat and the brothers are told, by the other hunter, Travis (Ron Lea), that eventually Jack will taste human flesh and then his transformation into the rugaru will be complete. Travis had killed Jack's father - another rugaru - 30 years earlier, but hadn't realised his wife was pregnant; the child was put up for adoption and it had taken Travis all this time to track him down.

Jack's situation - of effectively having a demonic force inside him, driving him towards committing evil - served as a metaphor for Sam's own situation; the parallels between the urges driving them to give in to their "powers" and the consequences if they did. Jack was born with the rugaru gene, while Sam was given demon blood the night the Yellow-Eyed-Demon visited him in his crib (and killed his mother). Will Sam turn into a monster like Jack? We will have to wait and see...

Metamorphosis started off as an old style "monster of the week" story but quickly developed into a solid character piece about the clashing personalities of Sam and Dean and the wedge that is being driven between them.

The ultimate on-screen realisation of the rugaru was a shockingly, bloody return to some of the out-and-out gore of the earlier seasons, but still achieved stylishly with a minimum of special effects.