First things first... I called it. I totally called it when Yui's chipped key was shown. The chip was stuck in the lock, just like I said.
It was honestly a pretty obvious choice, I feel.
However, it looks like it wasn't Yui's doing, but random friends of theirs that got ahold of the key and locket. I mean, that probably makes a lot more sense than Yui trying to open it, when she knew it wouldn't with her key, and that it wasn't the time to try, anyway.
And, damn... Yeah, Claude, the clod, finding out way too late about everything, I see. I mean, why did he wait until now to try anything, if he didn't only recently find out?
YOU CLOD!!!
And now, master vs student.