Interestingly,when someone else was trying to remember /locate The Mystery Of The Island by Isobel Knight on another site a few years ago:
One poster suggested:1chris_black
May 26, 2013, 10:48am Top
I've been trying to figure out the name of a children's book that I read years ago but I can't figure it out and google has been no help.
It was about a family who moved to a small Scottish island to work a croft because the father had been sick. Locals said the farm was cursed as it had quite a few owners and there was a ruined castle nearby that was supposedly haunted. Strange things start to happen, the father gets seriously injured and taken to the mainland (the mother goes with him) but the kids stay. They figure out that it's all related to a gang of smugglers because of pearls on the beach and everything rights itself.
This book 'Highland Fling' by Sybil Burr looks interesting itself.2diana.n
Edited: May 31, 2013, 6:35pm Top
Strongest possibility, so far: Highland Fling, by Sybil Burr: Per Loganberry, "Highland Fling, by Sybil Burr, published Westminster 1957. "In this suspense-filled adventure story, three youngsters explore the Scottish island of St. Bride and become involved with a secret hidden in an old tower." (HB Apr/57 p.182 ad)."
a search for 'Highland Fling' reveals that it was originally called 'The Saint Bride Blue' and is now an extremely scarce title:
http://www.abebooks.co.uk/Saint-Bride-B ... 0586963/bd" onclick="window.open(this.href);return false;