The island of Eilean Mor is one of the seven islets of the Flannan Isles, also known as the Seven Hunters, located off the coast of northwestern Scotland and named after Saint Flannan, an Irish priest. Apart from the only landmark of the remote location, a ruined chapel built in the 7th century by St. Flannan, there is a lighthouse, built between 1895 and 1899, at the island’s highest point on Eilean Mor, overlooking the west coast of Scotland. Designed by David Alan Stevenson, the lighthouse was built at a cost of £1,899 inclusive of the building of the landing places, stairs and railway tracks.

The railway tracks were necessary for the transportation of provisions for the keepers and fuel for the light, up the steep 148 feet (45 m) gradients from the landing places using a cable railway. The 75 feet (23 m) tall lighthouse was manned by a three-person team comprising of Thomas Marshall, James Ducat, and Donald MacArthur, with a fourth man rotating in from shore.

It was the transatlantic steamer Archtor on its voyage to the port of Leith from Philadelphiathat first noticed something odd about the Flannan Isle Lighthouseon the stormy night of the 15th of December 1900 and made a note in its log that its light was not working in that poor weather conditions. As the news was passed on to the Northern Lighthouse Board, the lighthouse relief tender ship Hesperus under Captain James Harvie was instructed to investigate the matter.

However, Hesperus could not sail as planned on 20 December due to adverse weather and the journey was delayed not to reach the island until noon on 26 December. But when Harvey and his crew finally arrived, it became clear to them that things are not normal and something was oddly awry. They were utterly shocked to find that the Flagstaff had no flag, all of the usual provision boxes for re-stocking had been left on the landing stage and more ominously, despite the repeated horns of the ship, nobody appeared on the shore to welcome them.

Immediately, a boat was launched that took Joseph Moore, the relief keeper, alone to the shore to investigate. After ascending the cliff he found that the entrance gate to the compound and the main door both were closed. On entering the living quarters, Moore noticed the beds unmade,the clock on the kitchen wall had stopped, alamp was ready for lighting, the table was set for a meal that had never been touched and an overturned chair nearby. However, there was no sign of any of the keepers. On his return to the ship, Moore reported his findings to the captain of the Hesperus and Harvie sent another two sailors, the second-mate of the ship and a seaman, along with Moore to shore to look for signs of life.

But after an intensive search of the lighthouse complex, they foundnothing but a set of oilskins, suggesting one of the keepers had ventured out in just his shirtsleeves. While everything was intact at the east landing, the landing platform on the west side of the island provided plenty of evidence of damage, evidencing the recent hit of a massive storm. The search party was awestruck to find that despite being over a hundred feet above sea level, a supply box had been smashed open and its contents were strewn across the ground. Moreover, iron railings on the side of a path had been bent and twisted out of shape, part of a railway track had beenwrenched out of its concrete baseand a huge rock weighing more than a ton had been strangely displaced. However, they did not find any clue for the three missing keepers of the lighthouse.

After receiving the report, Robert Muirhead, a superintendent of the Northern Lighthouse Board, who had originally recruited all three of the missing men, arrived on the island on 29 December 1900, to conduct the official investigation into the incident. After critically examining the oilskin that had been left behind,he concluded that Ducat and Marshall had gone down to the western landing stage and it was McArthur, the occasional keeper, who had left the lighthouse during heavy rain in his shirt sleeves. He also concluded that,till the dinner time on Saturday the 15th of December, all of themhad been on duty and after that, they had gone down to secure a box, containingthe mooring ropes, landing ropes and other items, which was kept in a crevice in the rock about 110 feet (34 m) above sea level. Unfortunately, at that moment, a huge wave rushed up the face of the rock with immense force that has completely swept them away. However, it is also possible that they were blown over the cliffs or drowned trying to secure a crane or something like that.

Nevertheless, the subsequent discovery of the logbook entries between the 12th and 15th December were more baffling. In the entry on the 12th, Marshall is supposed to have written that a great storm, the likes of which he had never seen before in twenty years, had hit the island. He also wrote that,when the storm finally struck the island, the usually quietDucat and the big, burly man McArthur, a veteran mariner with a reputation for brawling, were weeping in apprehension. While the second entry has all three men praying in the eye of the monstrous storm, the third and final entry, supposedly written on the 15th, states that the storm had passed and all was now calm. However, the existence of these logbook entries gave rise to the question, if the keepers were swept away on the 15th, who attended the logbook on that fatal day. Moreover, as there was no report of tremendous storms in the area during those days, the poor weather condition recorded in the logbook was either localized or were fake, injected several years after the disappearance of the keepers.

Leaving aside the fake logbook entries and the fanciful tales of being gobbled up by a giant sea serpent or whisked away by a huge seabird, it was argued that probably the men tried to leave the island by a boat and were eventually drowned. According to another theory, one of the men, probably MacArthur, the strong and sturdy man infamous for his ill-temper and brawling, murdered the other two in a blind rage, due to some unknown reasons, ditched their bodies into the sea and then threw himself off the cliffs. However, as no evidence of a fight or murder was found on the site and no bodies were ever recovered, these two theories remained forever as mere supposition. The most convincing explanation of the incident is that, while MacArthur was left behind to man the lighthouse, Marshall and Ducat went out to secure the supplies and equipment on the west landing and were swept away. But as they failed to return after a reasonable time, MacArthur became impatient, headed out to find them and was also eventually perished by the violent gust of the storm. While this theory seems to be acceptable and has the advantage of the advantages of explaining the set of oilskins remaining indoor, the reason for the closed door and gate remained unexplained.

In fact, nobody really knows what happened on that fateful night on the island of Eilean Mor and the real reason for the disappearance of the three lighthouse keepers will probably never be known. Till today, the mystery of the Flannan Isles remains one of the most baffling episodes in Scottish maritime history.