After a long cutscene, you'll have control of the party inside the house, this time with Lightning in the lead. You can explore, or analyze the TV to advance the plot. Eventually the house will be invaded by a variety of Sanctum troops. Collect the two Treasures before triggering the cutscene, and with it the final battle of Chapter 7. Note that you can't reach the boss with Physical attacks, so don't worry about Strength-adding Accessories, such as the Brawler's Wristband found before the battle. Defeating the Havoc Skytank will unlock Crystarium Stage 6.