This unexpected detour is not my first in the last two weeks. It's one of the most exciting things about writing a first draft, at whatever speed you decide to write it. Sometimes, your characters know better about what should happen next than you do.
Now I'm sounding like one of those kooky writers who tell you that the characters take over, and the voices in their heads, and that the words appear from nowhere, while they aren't looking. This all sounds kind of psycho but the truth is, there's some truth in all of these things. The characters don't *actually* take over, of course, it's your idea of them that does. As you write, and put them in a variety of situations, you imagine them more clearly. In that kooky talk - you *know* them better.
Where the writing comes from, well, that's a whole other blogpost, for another day.
Today's Nanowrimo wordcount = 33522 (about a day ahead of schedule, for what it's worth.)