Is that the only place with 2 dashes in a P tag
Code:
<p class="calibre3">(.+?\s--\s.+?)
Replace:
Code:
<hr class="sigil_split_marker" /> <h3 class="chapno">\1</h3>
I happen to use Sigil for this task, but Calibre will work fine with a small adjustment.
The Marker is what you split on.
I made it a H3 tag (chapno is the stylesheet entry)