answer:I went through a similar horror after a toilet leaked from the first floor onto the ceiling of a basement stall shower. The plaster fell off, the mold collected, the paint bubbled and buckled. Call the plumber, as I did, and if you are lucky, he can also tear off/down the damaged wall stuff, repair and repaint. It took months since he needed to caulk and then let the walls dry several times. He did, of course, start with the source of the water damage, which required a new toilet (and some work on the floor it stood on.) Nasty, brutish, long and expensive.