Q: Episode One is a new in the Half-Life story. Was delivering such episodes part of your plan for Half-Life 2 since day one of the sequel's conception, or was the idea born at a later date?

Robin Walker: We knew while we were building Half-Life 2 that we needed to find a way to get games to our community faster than every 5 or 6 years. With the success of Steam and the lessons we learned by updating our multiplayer games frequently during Half-Life 2's development, we felt like we could take the same approach on the single-player side. This was a conclusion we arrived at before Half-Life 2 was released.

Q: What particular challenges does penning a plot for an episode throw up, as opposed to penning the plot for a full sequel?

Robin Walker: It's the difference between running a marathon and running laps in a relay race. We set things into motion knowing that we're not going to resolve them immediately, so we want to make sure they have an actual destination and can stand on their own. Instead of wrapping everything up in one bundle, we have to stay several leaps ahead of ourselves. Each episode must both be self-contained and set up plotlines to be resolved or explored in the subsequent episodes. The nice thing for us about working episodically is that during the final polishing stages it's possible to see the whole story very clearly and make smart decisions about which elements need further development. This is much more difficult in a more traditional (non-episodic) game.