I mean, it has been established that you can convince Arthur of something with solid evidence and the robbing with apparently a key was solid evidence.

Good point. In Valiant, Arthur was convinced once he was showed the snake's head from the Valiant's shield. Another thing that totally bugged me about Arthur in this episode is how moronic he is regarding the whole Cedric business. It's really not like him to instantly abandon all guard around strangers, and being careless with stuff that he has been entrusted with.

That has totally slipped my mind! :p They had some very good scenes in The Moment of Truth and To Kill a King too. I really like that even when those were very brief scenes, it holds a lot of weight for me with regard to the eventual Arthur/Gwen relationship. But I'm really not happy with the latest episode though. :(