Plunge

"He'd thought, his whole time with the Flynn-Fletchers, that he understood Ferb better than maybe even Phineas. The second he'd put that hat on, though, he couldn't get a read. Ferb had shut down, and sure, he'd come to his defense a few times – reminding Phineas that he'd tried to stop them, calming Phineas down in the alley – but that was just who Ferb was." Post ATSD, one-shot