As the show's about to begin and all of Gotham tunes in, Terry admits to his mom and little brother that he's Batman. They laugh in his face. The show is postponed at the last minute, which sends Terry into action. Seems all of Ian's molecule scrambling has resulted in a body that can't sustain itself anymore. Ian's body loses its solidity and he falls through the floor and into the Earth itself.
Batman tries but is unable to help.
What doesn't make sense is that Ian never had this problem before. He walked on floors as he strolled through walls and never thought twice. The answer's never given. It's exciting to watch as Batman's secret identity is nearly exposed but once the episode's over and the logic police arrive, this house of cards falls apart. Some stories can't stand the pressure of their own weight.