This always happens when I work on a book. I poke and pick at the first 10 chapters or so. I work out the characters, I type some here and there then all of a sudden ... BAM... I know how the book should work, I know who dunnit, I know how it's going to end, and I can't wait to get to the keyboard.
That's what's been going on today. I've been writing like a fiend, going back and forth, working out plot points, laying in clues, and mapping out the next 5 chapters or so. The way I'm going, I'll have this wrapped up in a week, easy.
I never know when I start a book if it will be like pulling teeth to write it, or will it flow off my fingers? This one is FINALLY flowing...hooray!