The initial report from our new plumber is that the leak is from a cracked drain stack, and we may be replacing it from the bath tub all the way to the basement.
The rough translation for a home owner is, "kiss your three year old kitchen ceiling goodbye".
p.s. we have a new plumber because the old one didn't answer return our call. However, it may not be his fault, because Verizon's voice mail network broke.