In 1745, a treasure was floated across the water to Scotland in support Bonnie Prince Charlie and the Jacobite Rebellion. The first part of the gold ended up captured by Clan Mackay, a clan loyal to George II.
Another shipment arrived in Scotland in April, 1746. Seven caskets of gold. But it arrived too late, after the Battle of Culloden on April 16th.
Macpherson of Cluny had the secret of it's location. Hiding out in a cave at Ben Alder, he kept the secret even when Bonnie Prince Charlie joined him and after Charlie fled to France in September.
For the next eight years, Macpherson stayed in that cave, known as "The Cage," and used the gold to finance rebellions that came to naught. Bonnie Prince Charlie never saw any of it and blamed Macpherson for the loss of it.
After 1753, no trace of the treasure was found though the Stuart papers have a series of contradicting stories about the gold and one of the clans mentions French coins found in the 1850s.
This treasure could be used in a treasure-hunting game set between 1746 and today. It could also be mixed with the legends and myths of the Highlands of Scotland for a mystical game. The possibilities are there, ripe for the taking.