For centuries, the rocky island was only approached with fear and trepidation.
Hebridean shepherds ferried their sheep over to graze on the rich green pasture, but refused to stay a night.
When the waves crashed violently against the craggy cliffs, rain lashed and gale-force winds screeched across the Scottish island of Eilean Mor in the Flannan Isles, it was very easy to believe in the supernatural.
Some said an eerie aura proved the uninhabited island was haunted by spirits, “little people” and fairy folk.
Some said it was the ghosts of shipwrecked sailors, or the terrifying Phantom of the Seven Hunters, which lured men over the cliffs to their death.
Others said it was home to the Devil himself.
It juts out of the stormiest part of the Atlantic, making its lighthouse a literal lifesaver for passing ships.
The only man-made structure on the island, bar a tumbledown church, it’s now only known as the location of one of Britain’s greatest mysteries.
The year was 1900 and inside the lighthouse’s whitewashed stone walls, three men lived and worked, doing their very best to ignore any local superstitions.
If their gas lanterns flickered, kitchen pans jangled and hairs on their skin rose, that would surely be only the drafts from the howling gales.
Donald MacArthur, James Ducat and Thomas Marshall were used to such wild conditions and paid to brave them.
All three were experienced lighthouse keepers and this posting, on the largest of the Flannan Isles, in the Outer Hebrides, was a job they needed to feed their families back on the mainland.
As always, on the morning of December 14, 40-year-old Donald, James, 44, and Thomas, 39, chalked the blackboard to log the jobs they’d completed – the lamp was trimmed, the oil fountains filled and the giant lenses cleaned.
After lunch and steaming hot mugs of tea, the dishes were scrupulously washed. Then, all three simply vanished, no trace of them ever to be seen or heard of again.
Just like the thick fog which drifts in so perilously fast in these parts, nothing is clear about their fate.
Whatever did happen to them, stories have been passed down through generations and been immortalised in books, poems and even a song by Genesis.
Now, a new film starring Gerard Butler, Peter Mullan and Connor Swindells, uses the Flannan Isles lighthouse enigma as the basis for a psychological thriller called The Vanishing.
It weaves together temporary insanity, greed and murder for a dark and bloody explanation of what might have happened.
The characters in the film share the same names as the three missing men. But what is really known of the real-life story behind the trio’s disappearance?
“The truth is, nobody really knows what happened,” says Keith McCloskey, who researched the story extensively for his book The Lighthouse: The Mystery of the Eilean Mor Lighthouse Keepers.
He says: “That’s why generations have been so fascinated. We do know reports of finding an unfinished meal on the kitchen table and an upturned chair are rubbish, but because those details were first written in 1912 in a famous poem, Flannan Isle by Wilfred Wilson Gibson, people have mixed that with the truth for over 100 years.
“There were reports of highly emotive logbook entries, telling of one man crying and all three praying. It added great fascination to the story.
“But these very well written logbook entries first surfaced in 1965 in a book by a sensationalist American writer, so I feel they’re almost certainly bogus.”
According to shipping records, the first anyone realised something was amiss on the Flannans was when a cargo ship heading to Edinburgh from Philadelphia reported the lighthouse wasn’t working on December 15, 1900.
Stormy weather delayed the journey of relief keeper Joseph Moore, who reached Eilean Mor on December 26.
He found the entrance gate to the compound and main door both closed, and the clocks stopped.
One oilskin remained on its usual hook, suggesting one man had gone outside in shirt sleeves. But there was no sign of Donald, James or Thomas.
Joseph was so upset by what he found, he had to be taken off the island.
Three days later, Northern Lighthouse Board superintendent Robert Muirhead arrived to conduct an official investigation.
He found extensive damage to the west landing, a little harbour on the island, where iron railings were twisted and displaced, a block of stone estimated to weigh a ton dislodged and carried on to the path, and a life buoy torn from ropes.
He concluded that an “unexpectedly large” wave had engulfed the men and “swept them away with resistless force”.
The theory does not wash with author Keith, who has spent time on the island.
He says: “For me, the giant wave theory doesn’t work. It seems obvious, so the theory seems convenient.”
Keith believes there are more convincing theories behind the mystery.
Long friendships with lighthouse keepers have given extra insight into the unusual weather on the mist-wrapped islands and the atmosphere between workers cooped up together.
Keith says: “One lighthouse keeper told me the wind could be behind the disappearance of the men. He was 16 stone and was carrying a fridge one day and the power of the wind lifted him and the fridge, and carried him about 30 feet.
“Eileen Mor is very exposed – I’ve stood there. So his view was that two of the men were probably bringing supplies from the east landing, but it needed somebody just outside the lighthouse to help bring the winch.
“He thinks the wind took them over the wall of the lighthouse, which is very close to a 300 foot drop.”
Keith says there is another, much darker, theory.
He says: “The keepers told me you work with two other men and, especially if you’re on a rock lighthouse, you can’t even go for a walk.
“One of them has the power over the other two and if you didn’t get on with him, you’d have a hard time. It was a tinderbox environment, where tempers were easily lit.
“I’ve spoken to three descendants of Donald MacArthur. He had a volatile temper and had been stuck out there for two-and-a-half months.
“It’s quite possible he got himself into a right rage, a fight broke out near the cliff edge and they all went over. Or he murdered the other two and killed himself after what he’d done. That’s the theory I’m most convinced by.”
Meteorologist Dr Eddy Graham, of the University of the Highlands and Islands, believes notions of a powerful wind and fiery tempers are “a big bunch of baloney”.
He looked strictly to science for the answer.
Dr Graham says: “I used a new weather database, a model called the re-analysis data model, which goes back to 1873 and it was put together in recent years.
“It uses old weather records that have been digitised – like old barometers used to measure sea level pressure.”
Dr Graham analysed the detailed weather conditions on the days surrounding the three men’s disappearance. His findings challenge the date of the huge storm.
He says: “The final inquiry said the men disappeared on 15th, but I think it happened two days earlier. Because the storm on 13th was worse. It was a howler. Maybe not a hurricane but a proper, good winter storm.
“Between the Flannan Isles and the Faroes is the stormiest place in the North Atlantic and it’s a big long stretch of south westerly winds, running 2,000 to 3,000 miles over several days and coming all the way up from Bermuda and the Bahamas.
“As it moves north it increases speed because something called the Coriolis force increases the wind speed and turns the wind.
“I think somebody got in to trouble, the others went to help and a freak wave washed them away.
“There was damage at 100ft above sea level on the platform, so you have the Atlantic running mad for several days and pretty good anecdotal evidence that there are freak waves two or three times the height of normal waves.
“So from a scientific point of view, the only theory that has any traction is a big storm and there’s really good evidence of one. I think that’s probably what happened.”
Maybe the solution is as down-to-earth as the power of the wind or a giant wave.
But that doesn’t explain why, in the years that followed their disappearance, other lighthouse keepers claimed to have heard voices in the salty air screaming out the names of lost Marshall, Ducat and MacArthur.
The Vanishing is in UK cinemas now.
THE VANISHING is also now available on digital platforms