Help with a plot?

I need to have the first three steps of the snowflake method done for my not yet started novel by the day after tomorrow - the tenth. Now, I had an idea before, and it sucked. I was trying to combine twenty-bazillion story ideas (all of which were lacking) into one. It didn't work.

So now I did something which I think might be better - I thought of a completely new idea. But as you can see, it's very undeveloped and needs a lot of help to get off the ground. Preferably before the day after tomorrow.

Here's what I have so far:

Ever since her 2 year old brother was abducted from their very own garden, leaving only a typewritten note with the words "[I have no idea]" behind, [fmc]'s life has not been normal. Five years after the incident, to the day, she finds a nearly identical note and a letter from 'E. Gullivan' on her front doorstep.
Meanwhile, [mmc] is baffled by the recent string of disappearances in his extended family - the first and most prominent, that of his wealthy and eccentric aunt.
When he meets [fmc], [something which I have no idea about happens]. Together they [verb], ride hot air baloons, and find clues in books older than them to unravel a sinister attempt at earning money through lives.

As you can see, this story sucks. It just DOES. But it's better than radioactive waste causing wings, secret societies, and sweet sixteens all mashed into one book, right?

So, I ask you for help. If you do help, your idea (if I use it) becomes legal property of me or whatever. So when you post, think of that first. xD Do you have any ideas on what should happen in the story?

If it helps, fmc will probably be called Jen, and I'm not quite sure about mmc. Fmc's brother will be called Tobias and he'll have a twin sister called Claire. They'll be two and a half at the age of kidnapping, seven and a half at the time of the book. Mmc is video-game addicted, snooty but sorta shy, and his parents are rich. Fmc prefers to be outdoors, is confident but rude, and her mom is an interior designer.

Any help would be GREATLY appreciated. :3

I sense that MMC owns a Wii and like a bajillion games.

But that probably isn't any sort of help. XD Hmm. So what sort of suggestions exactly are you looking for? Just events that might happen in the story, really?

You guessed it. xD

Yeah, pretty much. I have no idea what'll happen apart from the backstory - and even that sucks. -shrugs- I don't know.

Well, fmc should not fall in love with mmc. Unless he never lovers her back, but does realize it at some point in the story. In which case it'd be interesting to see him crushing on a different character.

And this E. Gullivan guy seems like he might be related very distantly to the mmc, or at least know his family . . . hmm . . . it'd be interesting if mmc were to recognize him later on in the story, but not as the killer. You could make it seem like someone else is the killer first, and have them chase that person before figuring out that E. Gullivan really did it.

If he did. XD Because he might be just a guy who had to write those notes.