so I broke out the black light and....

[kb2yjx]

I guess the previous poster and I have read conflicting articles about the use of bleach and cats. I have used it for years, and the cats have had no problems with it. However, AMMONIA is NEVER to be used, since there is the smell of it is close to that of urine. Whatever works best in your situation! I do agree with the suggestion of the rubber glove and checking for urine. When we had our floors refinished, and pulled up the wall to wall carpeting, were we surprised to find that a certain corner had been a favourite spot of the previous owners' cats' to pee on. The floor had discoloured to a black colour. After the floors were done, we put a chair there to hid the discolouration!!!

[RobLynn]

If the previous owner had cats, in the same spot, where urine could get on a wall, it could be the reason.

They say when a cat pees on a vertical surface, that they are marking their territory (I could be wrong, but this is what the vet told me).

Maybe repainting that area after a very good cleaning. If that don't work, you may need to replace the drywall in that area. I don't mean the whole room, just the affected area.