I'll take a stab at this, although house plants aren't my best field. For one thing, how wet or dry was the soil? I'm guessing that the plant was either over or under watered. I would cut away the very worst leaves, the one in the 4th pic, anyway, so that the plant can use it's energy to help the other leaves recover. I don't think you're loking at disease on the leaves themselves, if anything, it could be root rot from overwatering.