Arthur didn't go back to the inn to meet up with his two companions, instead, he headed toward the royal castle, where the current ruler of the kingdom current is.
He never thought things will become problematic this quickly, nonetheless, debts must be paid back in full and what he's about to embark on is not only dangerous but reckless too.
He didn't know how such a thing is possible but he's not going to sit around and try to decipher the past. He had one goal for now and that's to eliminate the target.
Fortunately, with the disappearance of the system, the oath was no more so he's able to use weapons, which will greatly facilitate the mission.
As one would expect, the castle was heavily guarded but the soldiers weren't that strong so it wasn't hard to get rid of them. He chose the time when the sun was going down and the soldiers replacing their comrades to sneak inside.