If it's not Plankton who stole it, I'll eat my shoe (and I know I don't wear any shoes you simpletons!). But if you want a curveball, uhh, maybe Bubble Bass or Mrs. Puff? Puff was the culprit of our first ever mystery, it'd make sense to bring it full circle even more. I also didn't see her when the lights were out so...interpret that how you will. Whatever, I'm just glad I don't have to do another one of these mysteries ever again.