He ambushed the party on their way to Castle using a series of clay golems. These golems were created for Captain Thorpe, the commander of Dunavar's Spire, which is a mysteriously large order for a mere Captain to sign off on. Mind control may or may not be involved.
After the golems were defeated he fled, and later briefed the other Dark Ancients on his view of the party's ability to ruin the group's plans. He heavily underestimated them.