I need a prophecy! Please help!

Ok, I'm collaborating with a friend of mine to write a fanfic, and we need a prophecy. We already know what we will be doing on our quest, we just need the prophecy for it.
We have a son of Zeus, a son of Hades (although the son of Hades technically hasn't been claimed yet; he will be claimed later in the story), a daughter of Athena, and a daughter of Hermes. We also have a mortal who can see through the Mist, and somehow is able to get through the magic boundaries (we still haven't decided what to do with him... we just know that he's going to be important to the story).
The story takes place 20 years after all the campers from the Percy Jackson series have died.
The Romans and Greeks have, once again, separated.
We are going to be rescuing a kid who has been missing for just short of a year. He has been captured by a woman (no clue who yet) and a strange, male monster that can turn into pure darkness to hide within shadows... IDK if a monster like that exists, but if not, give it a name!
The kid who is going to be rescued is a son of Hermes. The two who captured him are working for some sort of "Master" who has a deadline for the woman to create some kind of potion (so I'm thinking somewhere along the lines of Medea for her) for him to use to take over the world. We will not meet the Master in this book, it will occur in the second book.
Anyway, please help me come up with a prophecy!