I'm planning an adventure where there's a succubus afoot causing trouble, but while people are suspicious a demon is responsible, no one knows for sure. Bad stuff just keeps happening. The party needs to meet various characters in the town, gather clues, and figure out the common element, and then confront the succubus.

Thing is, the party has a paladin, and I want to make sure that the mystery isn't subverted by him deciding on a lark to use Divine Senses when they meet the disguised succubus. There will be other little demons around working for the succubus, so it's not like the ability will be useless, but I want a way for the succubus to hide her true nature without it being wholly unfair to the PCs.

Ideas?