Why has the Book 5 saga stopped abruptly?

When I started the Book 5 saga I never intended it to go on so long. Probably ending when our adventurers got to Scotland, I meant to stop and leave them on a knife-edge but I got carried away. It was enjoyable but I was drifting!

I finally realised this and thought it was time to step back and to see how the structure would best fit into a novel, but also into the 5th novel in The Wheel of Eight series.