Minor update: I have actually started writing, and have written down notes for up to five books in the series so far. I've done quite a bit of research as well to help make the story seem as realistic as possible, in the universe I've created of course.
Just to give you an idea, the general storyline is this: ritualistic appearing murders are happening in and around the DC area. A formerly British FBI agent in the FBI's homicide division (he's a naturalized citizen) is forced to team up with a mute female FBI agent, after his partner was killed and hers had retired, because he's now the only active agent in the Agency who understands ASL (which she speaks due to being mute, naturally, and he understands because he served in the Army and learned it after a friend in the service became deaf due to an IED explosion). They clash at first, of course, but slowly become partners and even friends as they try to figure out why the murders are happening, only to discover that they're now embroiled in a world where myths, legends, and magic are a hidden reality and are policed by a worldwide agency which tries to keep that fact hidden from the "norms" so as not to incite a worldwide panic. The working title (and name of the agency) is The Bureau of Extranormal Affairs.
There's other major plot points, of course, but one, I don't want to spoil the entire plot, and two, my writing thus far has only come in fits and spurts, so I'm still not positive I'll finish it, despite having ideas for as many as five novels in the series. One thing I have realized about my writing (and which I think is responsible for why I never finished anything before) is that I tend to get ideas for scenes in the story that are for MUCH later in the overall storyline, which means writing in a linear fashion is virtually impossible. Before I always tried to keep writing linearly, but now I've realized that if I DON'T write down whatever scene popped into my head, by the time I actually get to that point in the story I might have forgotten whatever I had planned, so now I'm actually making the attempt to write things down as they come to me. Even if it turns out not to fit in the story by the time I get there because I've made changes to the plot, at least I'll have it written down in case I CAN get it to fit. If it doesn't, it'll become an outtake, essentially.
I've been trying to write at least a little bit every week, and come November I plan to actually buckle down and participate in NaNoWriMo in the hopes that it'll fully kick-start the writing process. One advantage I seem to have is that, due to all the time I spent writing fanfiction, my writing style is actually decent, and I'm starting to be able to figure out where I can trim areas down so as not to be horribly wordy. I don't know if this will ever come to anything, but I can say this; IF I manage to finish this, I am going to try to get it published. The only annoyance I have in that regard is that I'm going to have to get it cleared by the government before I can do that for pretty much the rest of my life; since this novel was sort of inspired in part by my work with the government as a contractor, I have to have it reviewed to ensure that nothing sensitive is included in the manuscript, and the same will go for any future books I write. I don't know yet if I'll try to self-publish or if I'll shop it around to publishing corporations, but since I'm nowhere near that point I've put it on the back burner for now. So... wish me luck, I guess.