Nancy Drew Phantom of Venice Hint?

Ok, so I caught Nino, and called Sophia. I went to the propane tank thing and got the key out. Now I'm stuck. From looking at the online hints it seems like there is something left of the Costume Shop that I'm suppose to be able to use the key to open. I CAN'T FIND IT!! I've spent hours looking around the costume shop and there is NOTHING left (or right) of it! My magnify gl will light up sometimes (when I have the key in my hand) but it won't let me click on it! Please help!