It had been mentioned before, but Damien didn't leave August to figure it all out on his own.
He'd left clues all throughout Fort Halleya that would eventually lead him to the right place.
It obviously wouldn't be easy, but it was absolutely possible, even with the particular uniqueness of Damien's current hiding place.
Damien believed in his son, and August believed in his ability to read his father.
Making it out of the crowd was a problem at first, but for geniuses who put their mind to it, evading regular civilians wasn't a problem at all.
In a situation like this, they were permitted to use their power, weren't they?
August was able to maneuver in such a way that he could avoid all prying eyes without a problem. Valerie was more high profile, but after seeing her performance in the arena, hardly anyone was willing to stand in her way.
