One barbarian at a time was brought before Mandra when they were caught. They were questioned on their communication methods, signals, names, and favorite food just to confuse them.
As expected, the barbarians came up with different methods for how they communicated or were supposed to communicate with their allies outside the city. There were bird calls, hoots, arrows with specific fletchings, and some even had notes prepared.
They were lying.
Mandra's Eyes of Truth weren't even needed to determine that, but they helped narrow down the parts of truth the barbarians had subconsciously or actively sprinkled in to make their lies more believable.
Yan knew it was too early to celebrate since this was merely the first step of Zach's plan. But they had fulfilled the necessary condition to move forward with the next step. They had found out how the barbarians were supposed to communicate with their allies outside the city.