Thanks to everyone for your heartening and useful comments. Yes, once again, I have demonstrated how easily I get sidetracked by 'intellectual' problems when they never really matter much in the construction of a book. They do function rather nicely as avoidance items though. Of course you don't need to know what you're doing when you sit down, in fact I think it is positively bad if you do, as this will stand in the way of interesting progress. For myself though I definitely need an emotional hook to get me going. I only have one scene so far in which that exists, and it isn't the beginning of the book, but I think I will make it the beginning anyway as otherwise there won't be one. Fingers crossed all else will flow from that point.