The castle was a mess, with guards running around, yelling, "find the assassin!"
Damian was an assassin who tried to kill the Duke, yes, but he was not the assassin who killed the servants. They put the blame on him, which did not matter.
It was all fake. The assassin who killed the servants was probably someone under the Duke's command, perhaps his daughter, and they did that to lure someone from Glen's noble house to start their plan!
They did not know who Damian was, but if Neil and Glen agreed to send him, then he had to be someone from their family, or someone close.
"Everyone is looking for me, and where can I find the Duke?"
The situation was not looking good for Damian, who had an army of guards looking for him, and a severe injury on his abdomen. He needed to rest and properly heal, but he also needed to find the Duke.