The second scheduled DLC for Heavy Rain has been put on hold, unfortunately. According to Joystiq, the DLC is on hold indefinitely while the team focus on making the game Move-compatible. Not much details about the second episode has been revealed, except that the Origami Killer is a playable character.
According to Quantic Dream’s Guillame de Fondaumière, Sony encouraged them to focus on the Move-compatible version of the game more than the second episode. de Fondaumière also indicated that they’re likely to move on to their next project, after completing the Move version, meaning the second DLC may never see the light of day.