Zero Sum is the second Skinner-oriented episode in the x-files. Avatar was the first and the story for this episode continues on the theme from Avatar, of Skinner being blackmailed by the cigarette smoking man. The storyline, however, continues on from Memento Mori, dealing with Scully's cancer. Scully(Gillian Anderson), actually takes a break from this episode and we never see her. Mulder says that she is undergoing testing in the hospital. An episode just isn't the same without her. Even so, Zero Sum is a tight, suspenseful episode, leaving you on the edge of your seat, wondering whether Agent Mulder will discover Skinner's part in the cover-up of the x-file. The music by Mark Snow sets the mood very well. Mitch Pileggi does an excellent job when asked to take on the bulk of the acting. He's doing unethical things in order to help out Scully. The cigarette smoking man also has a larger part in this episode. It is quite interesting to see the slow deterioration in his relationship with the syndicate. You see it begin in earlier mythology episodes, and it continues in Zero Sum, which leads to certain events in a later mythology episode. I like to see continuity like that. It's not often that you see the cigarette smoking man rattled, but Skinner manages to do that to him. Overall, Zero Sum is carried well by Skinner and Mulder with absence of Scully, helping us delve even deeper into the mind of Skinner, and see what lengths he'll go to to help out his friends.