Well not entirely. You're thinking too small. So if the Hethian somehow learned of the traitor among the mists of Blackquil, because I mean, they decided on Dulvac betraying the kingdom on top of a roof in a town. That's pretty noticeable. Any good tyrunt kingdom would attack to avoid their secrets from being discovered. While fighting, outside of Blackquil, Prince Thomas get's captured, (outside of Blackquil) and is then used by the Hethians as a bargaining tool. To be honest, I feel like we haven't been putting as much emphasis on the Hethian ingdom's power and well evil as a whole.
Just being able to find out and free Prince Thomas is making the conflict, too easy. It would add an interesting twist. We just need to present all of this right.