Maggie, a curveball may be just the thing! I think it was Raymond Chandler who said that if the plot is flagging, have a guy come into the room with a gun. It sounds like you're maybe telling a lot of back story, which may be more relevant to you than to your readers, or you may be writing a very detailed plan, rather than progressing the action? You might want to watch the relevant parts of Harry's How to Write video course (if you haven't seen it - or re-watch if you have). He has some great ideas for getting out of a rut.
Thanks Karen, I'll watch it. Part of the problem is that I haven't done any plotting beforehand - only decided to do NaNo 3 days before November 1st. I'm dithering about who to kill off next so focussing on characterisation via conversation because that's easiest to write. But I think I've found a way in, just need to get my ducks (characters) in a row (or perhaps a row - I think a good fight is what they need). Sorry can't resist.