Peter had known, the minute he had really started talking to Gabriel, and had gotten past his own confusion and disturbed feelings about being here, that something was wrong. He knew his brother well enough to know when Gabe was upset, and the vibe he'd been feeling even through the computer screen had told him that the older man was NOT okay. He didn't know just how bad Gabriel was, right then, but he wasn't going to take any chances that he might be beyond any sort of real help. He was going to help his brother calm down, and then the two of them would figure out how to deal with things, and maybe even get home. That would be nice, definitely.
Closing his eyes, he focused on his brother and on trying to find him, and unconsciously something activated deep in his mind, seeking him out and telling him exactly where the older Petrelli was situated. Nodding to himself, Peter breathed out a sof sigh before moving down the hallways he could see in his mind's eye, finally finding the correct door and knocking. After all, as much as was going on, it didn't hurt to be polite, right?