In lowland Scotland we associate scary stories and the presence of the dead with Halloween, but in the Northern Isles all those customs belong to Christmas.
It began life not as a jolly day for children but as the feast of the returning dead: Yule.
At Yule a truce was declared with the living, all work on the farm was stopped and large quantities of strong ale were brewed for the feast.
Now hauntings were at their peak and uncanny things walked.
Viking undead, with their supernatural strength and hunger for flesh, were not to be trifled with - they could tear your roof or your head off at this time of year.
On Tulya's E'en, seven days before Christmas, the Trows [trolls] were granted permission to leave their underground homes "in the heart of the earth and dwell, if it so pleased them, above the ground." , so the sign of the cross had to be made on everything.
According to folklore, the Trow becomes more active and more dangerous as Yule approaches - just like the undead of the Viking sagas.
At this point it was believed that the undead were allowed to leave neolithic mounds and barrows to trouble the living.
Even Orkney's standing stones, the Great Ring of Brodgar, the stones of Stenness, might be seen leaving their ancient places to go for a drink, dipping down to the waters of burn and loch, nodding to each other as they progressed, like Ents moving from a stone forest.
Tom Morton explores the spookiest time of the year in the Northern Isles.