Published by Arlington Books in 1975.
I have read this quite some time ago and can't really remember all the details any more, so I shall copy the blurp. It is an easy and enjoyable read, 160 pages, ideal for communting.
If Emily hadn't gone to Annie Richmond's party, she would never have met the impossible irresistible Rory Balniel - never have married him and been carried off to the wild Scottish Island of Irasa to live in his ancestral home along with his eccentric mother, Coco and the dog, Walter Scott. She'd never have met the wild and mysterious Marina, a wraith from Rory's past, nor her brother, the disagreeable Finn Maclean; never have spend a night in a haunted highland castle, or been caught stealing roses in a see-through nightie... Yes, it all started at Annie Richmond's party.