My rating is an attempt at objectivity. Objectively speaking, this is a very well-written romantic suspense, heavy on the romance. I believe it to be everything that was beloved of romances in the 60's and 70's. It was very well plotted and a great deal of care was taken with both atmosphere and characterisations.
Thus ends objectivity. I disliked this book. It is the embodiment of everything I find tedious in romances, in spite of wanting to enjoy them. The whole misunderstanding / lack of communication trope makes me want to set fire to the book as I'm reading it. It would take an emotionally neglected and abused protagonist to find the romantic interest in this book romantic or heroic in the least. He was vain, arrogant and stupid. She was just stupid, although I give her credit for being a smart-ass.
The setting for the first half of the book was England, and the second half in an Australian opal mining town, during a time before combustion engines and electricity were a thing (no specific date is ever named in the book). I thought at first this would be a saving grace, because I'm moderately interested in opals. But Holt was apparently obsessed with them, and her characters were mad about them. There was so much obsessing and evangelising about the damn opals. Holt was too heavy handed and went too far; by the end she'd almost killed any interest I had in them at the start.
A true connoisseur of the romance genre might enjoy this for the nostalgia if not for the good story behind it (and it is a good story). Me, I'm going back to my wheelhouse of murder and mayhem for awhile, before getting back up on this genre-horse.