Cyr alternative plan
I'll risk repeating myself in stating that I don0t yet know all the circumstances, but my suggestion would be something like this:
Send open letter from Bairdéir to Maor that states that sense of fear and distrust has been tracked to the lair of Daoine deBith operating within in the city. This goes in hope that someone will intercept it and react on it.
Second avenue of attack would be covertly getting the letter of warning to Maor that states there is assasination attempt brewing from Radharc, with assassin already within his own dungeons. This assassin was brought in the house only so he can get to know inside. The plan was to let him escape, and voila, he escaped! Either sign it as Bairdéir or find, which I admit is unlikely in this short time, loyal servant that Maor would recognize and sign him. Ideally, letter should appear to Maor without anyone giving it to him, maybe falling from the ceiling or appearing on his chair so he sits on it via some serious sneaking or disguise.
Third and final is Gavril giving hints that he is dissatisfied in Bairdéir service, his leg giving him trouble and Queen not listening to his needs to be a teacher in Bairdéir academy. That he is looking for a place to be his own man and that he is willing to consider alternate employer offer. All this could go at the same time and in the meantime we can try to track deBith in the city. I can go on for a day or two more if need be.