Chapter 226: The War that Decides the Fate of 'The Bridge' Part 29
Gilbert started suspecting the triplets when they learned the Assembly of Freedom is currently amassing their army to attack the Daze Village from their supposed spies in their enemy's force. In the first place, no one other than them and the staff could enter the Wing House Auction House's upper levels.
Needless to say, they let it pass because they were pressed for time.
Secondly, despite the fact that they used the underground passageway to evacuate, a significant number of soldiers from the Assembly of Freedom still waited for them at the exit as if expecting already that they were coming.
Indeed, they can assume that Wesley knew about this place. But why would he specifically send men waiting at the exit when he could just use the building above to enter the underground passageway and chase after the evacuating people, right?
