It is one of the greatest seafaring mysteries of all time and is currently gripping film audiences thanks to Kristoffer Nyholm’s thriller The Vanishing.

Now a new book could help solve the disappearance of three lighthouse keepers on the Flannan Isles – and it originates from beyond the grave.

Archie MacEachern, who was himself a keeper, died in 2005 at the age of 95. But his widow, Anne, decided to publish his recollections of life on the desolate islands, which are located off the Outer Hebrides.

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The work, called Archie’s Lights, is also shedding new light on exactly what happened to James Ducat, Thomas Marshall and Donald MacArthur.

It was Boxing Day in 1900 when it was discovered that the three keepers had vanished from their lighthouse.

A search party found, after climbing 160 steps up a 200-ft cliff side, an uneaten meal on the table and an over-toppled chair. All the clocks had stopped. But there were no keepers.

To this day, the mystery has never been solved – and remains one of the most puzzling in Scottish maritime history.

Stories abound about what became of the men. Some assume they were swept away by a freak wave, while, according to rumour, one keeper murdered the other two and then threw himself into the sea in a fit of remorse.

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In another story, a sea serpent – or giant seabird – carried the men away. It is also believed they were abducted by foreign spies or aliens.

However, Mr MacEachern, who served twice on the Flannan Isles and whose father was based there, had no doubt the disappeared keepers were trying to save others when tragedy struck.

He was told by a local of debris from a wrecked Norwegian ship that appeared soon after the disaster. Bodies were also buried in the machair.

The book records his thoughts: “It was known from reports that hurricane force winds were blowing on December 15. My theory is one keeper, wearing his oilskins, had gone up the tower to fill in the log.

"He went on to the balcony to check the wind and caught sight of the topmast of a sailing ship being driven for the cliffs. It is likely a second keeper was outside, also dressed for the weather. The third man was in the kitchen.

“The ship was only visible from the balcony. Clearly, she was in imminent danger. The keeper on the balcony would have run downstairs shouting: ‘Ship in trouble, lads! Come on! Quick!’

“The cook ran out to join the others, not waiting to put on waterproofs. Their immediate reaction was to race to the aid of a ship.

“They knew that if they could get a line to the crew, there might be a chance of saving those on board.

“To reach them, they would need the crane on the upper platform. While they were kneeling to loosen its clips, a wall of water raced up the rock face, snatching them from above.

“As the cascade retreated, their bodies would be tossed into the sea. The ship would have broken up very quickly.

“Having considered official reports, and my own and father’s experience of the Flannan Isles, I am left in no doubt – the three men were attempting to save other lives when they lost their own.”

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Although Mrs MacEachern, now 81, has never put pen to paper before, she – in Archie’s Lights – has captured the solitary and often dangerous existence of those who served with the Northern Lighthouse Board and were devoted to the maxim “For the Safety of All”.

She said: “We were married for over 30 years and I collected a lot of stories, because Archie was much older than me.

“The men on the lights needed to have the right temperament and be resourceful, patient and, when it was required, courageous, because it was a dangerous occupation.

“Some of the keepers were annoying and when you were in close proximity to them for weeks on end, it must have been very frustrating.

“The Second World War was a very difficult time because Archie and his colleagues always wanted to rescue people and prevent tragedies. But sadly, there were times during the conflict when they were powerless to stop these things happening.”

Mr MacEachern’s service as a keeper lasted more than 50 years.

Mrs MacEachern added: “Archie was one of a group of remarkable men who showed dedication to their duty, but whose role has pretty much been forgotten. I wanted to record the wonderful work he and the other keepers did.”

Today, the mystery of Flannan Isles has found its way on to cinema screens.

Scottish actors Gerard Butler and Peter Mullan team up in new psychological thriller The Vanishing, with Butler playing Ducat and Mullan taking on the part of Marshall.

Archie’s Lights is available from Whittles Publishing in Caithness.