Heavy Rain. He indicated that he "wouldn't want to spoil the story" as it will surprise people due to its unusual-for-a-video-game nature. Eurogamer speculates that the demo will therefore most likely focus on the game's mechanics.
Apparently, the video that was released yesterday is a separate episode that is unrelated to the main plot, which prompted the question of whether there will be DLC episodes in the future. Cage agrees its a possibility, but concedes that it is simply too early to talk about. The interface of Heavy Rain is "entirely contextual" and therefore open to the possibility of other stories.
Our very own Jem Alexander just got some hands-on time with Heavy Rain at LGC, so stay tuned for more details about this PS3 exclusive!