Well, thanks to a lot of help from you guys and the fact that I find it hard to give up, I finally did it!!
Frankly I didn't understand about half the answers I got so I started digging. I didn't learn much about CSS or HTML in the process but I learned a lot about the editor in Calibre. Well, maybe not a lot but more than I knew.
Most importantly I learned that it has a help file, which I didn't know before. I'm not sure that would have helped me but I used it to look up things described in the answers you guys gave me that I didn't know about, such as how to merge pages, etc, and I now have a repaired book.
Unfortunately I'm nearly done reading it but this was more about knowing how to fix that sort of thing than it really being a problem, so that's okay.
I had another book with a related problem and I learned enough in the process to fix that book as well.
At the moment I'm feeling pretty good. That'll last till the next thing I can't figure out. But that's just life.
Thanks again for your help. It worked.
Barry