Co-writing Checkpoint with Doug Petrie and creating the mysterious Knights of Byzantium

We went through an interesting process of splitting it up, in which we said, "You take the first half, I�ll take the second half." There was no thought or finesse or co-ordination at any point. We split it right down the middle. I wrote half and he wrote half and it was simply the luck of the draw who got to write what. It was a great experience, we both had a great time. In fact, I have split an episode with Doug again this season (Flooded) and one with David Fury.

The Knights of Byzantium was an idea I think Doug Petrie had. We originally called them the Knights of the Cruciform Sword, which was some idea that Doug had come across somewhere. I think it might have been an actual historical group, and we just sort of fell in love with the name.

For a while, we were calling them the Cruciform Swords and then Joss once referred to them as the Cruciform Ducks, which was like a slip of the tongue, and then they were the ducks � for a long time. We would just say, "Okay and then we�re going to need some ducks here."

It was just a very cool idea to introduce a new element that we hoped would end up being a major element through the season. Towards the end it ended up working out.