"Despite Dean's directive to forget about looking for a cure for the Mark of Cain, Sam continues to do research. Dean suspects Sam is hiding something but decides to focus on a new murder case where they run into Cole. The three team up and learn a Khan worm is infecting men and turning them into murderers. Unfortunately, the worm makes its way into Cole."
This was a good episode. We see Cole again, and he has finally figured out that the brothers are not the bad guys. This episode we see Sam fail in the face of a win. Dean figures out how to get the worm out of Cole without killing him, but the solution comes a tad to late for Cole's buddy who was just killed by Sam. A solution a couple of minutes faster might have saved them both. Strangely enough, Sam seemed a little upset by that, but not as much as usual. Whereas Dean, who bears the mark of Cain, seemed to be trying harder to find a cure all along when Sam just wanted to kill them. Kind of strange that Sam seems to have more of a blood lust than Dean.
