Well, 18 months later, spurred on by the fact that reality seems set on stealing my plot lines, the long-awaited book has finally been released into the wild. You can get it, as an eBook or paperback, here:
In the UK:
In the US and Canada:
In Australia and NZ:
If you are typing Brightwater into the search bar, for some reason Amazon Australia separates it into two words and you have to select the all-one-word version.