This is the story of the world's greatest-ever lighthouse mystery, and a possible solution to explain it.

The following details are recorded in the journal of the Northern Lighthouse Board.

Eilean Mor is one of the seven uninhabited Flannen islands twenty-one miles west of Lewis. Its coordinates are 58°17.3 North 07°35.4 West. It is a rock no more than 500 yards across in any direction. It has a reputation of being haunted, and according to the Ancient monuments Commission, its only permanent structures in the past were two bothies of Clan McPhail, the existing remnants in 1899 being a ruined chapel and dwelling.

In 1899 a brick lighthouse 23 metres in height was erected at its northern end giving an elevation of 101 metres. A light of 100,000 candle power flashed once every thirty seconds and was of sufficient strength to be seen 20 miles off.

In December 1900, four men made up the permanent staff of the installation: Head Lighthouse Keeper Thomas Marshall, Keepers Joseph Moore and James Ducat and Occasional Keeper Thomas McArthur. They worked a roster which involved three men being present on Eilean Mor, the fourth being on shore leave. There was no means of communication between the lighthouse and the shore. At the time of the tragedy, Keeper Moore was on the mainland on rostered leave scheduled from 6 December to 20 December 1900.

On the night of 15 December 1900, Cpatain Holman, master of the freighter SS Archtor bound for Leith, noticed that the Eilean Mor light was out and reported the fact by wireless to the ship's owners. By an oversight, they failed to notify the Northern Lighthouse Board.

The duties of Occasional Keeper Roderick MacKenzie, attending the nearby Gallen Head light, included checking from time to time that the Eilean Mor light was functioning correctly, but he failed to notice the outage due to poor visibility.

The return of Keeper Moore to Eilean Mor was delayed until Boxing Day 1900 because of bad weather. Upon the approach to the island aboard the supply vessel Hesperus, it was observed that no preparations had been made for the tender's arrival: no empty packing cases or mooring ropes were ready at the jetty, there was no sign of life, and accordingly Moore was sent ashore to scout the situation.

Moore saw tremendous damage to the handrails and retaining structure for the lighthouse boat. The main door and entrance gate to the lighthouse were closed, and the boat was correctly stowed. The lighthouse interior was neat and in order except that the kitchen door was open and a chair with a uniform jacket draped over the back lay overturned at one side of the kitchen table. The table had been laid for a meal and items of food were ready. The kitchen window provided a view over the sea northwards, but it would not be possible from the kitchen to see work being done at the waterfront, nor would shouting have carried to the kitchen from there. From a rack in the passageway, two sets of boots and oilskins were absent, a third set was hanging from a peg.

The wicks of the lanterns had been cleaned and trimmed, and the lamps filled with oil ready to be lit after dark. Of the three duty keepers there was no sign.

Keeper Moore called up the captain of the supply vessel, and the two men now went through the entries in the logbook. These read as follows:

"12 December. Gale N by NW. Sea lashed to fury. Never seen such a storm. Waves very high. Tearing at Lighthouse. Everything shipshape. James Ducat irritable.
Later. Storm still raging, wind steady. Stormbound. Canot go out. Ship passing sounding foghorn. Could see lights of cabins. Ducat quiet. Donald McArthur crying.

13 December. Storm continued through night. Wind shifted W by N. Ducat quiet. McArthur praying.
Later. Noon, grey daylight. Marshall, Ducat and McArthur prayed.

14 December. No log entry.

15 December. Storm ended, sea calm. God is over all."

In evidence to the Board of Enquiry, it was shown from the meteorological records that there had been no storm at Lewis, twenty miles away, over the relevant period.

The lighthouse journal was intended to record the weather, tides and barometer readings but not what mood the lighthouse keepers were in. Therefore mentions in the journal that "Ducat was irritable", "Ducat quiet" and "McArthur crying" indicated a very serious problem on Eilean Mor.

Moore told the Board of enquiry that he had never known any of the three men to pray, not to mention hold a prayer service together. Fear of a storm, no matter how violent a storm, in a well-found lighthouse was unlikely to have turned them all to religion. Something that happened over those four days of 1900 led them to fear not only for their lives, but also their souls.

Yet the Board of Enquiry concluded that the three men must have been washed away by a monstrous wave. This was widely considered unsatisfactory because the sea conditions over the four days were placid. This verdict also required the duty keeper in the lighthouse to have left it in breach of the regulations, to have carefully closed and locked the main door and entrance gate behind him before he proceeded to the jetty to warn the other two keepers that there was a monster wave approaching, which of course they were supposed not to have noticed for themselves.

The true explanation must have been realized by officials of the Northern Lighthouse Board as they reviewed the evidence, but they could not have even hinted at it in their verdict.

12 December was the day when these three lighthousemen knew the terrible danger in which they found themselves. It was then that they became upset and found the need to pray for salvation, singly and together. They saw something which, as men who knew the sea, they knew could not be.

A strong gale, the like of which none of them had ever see before, was blowing from the NNW. The sea was lashed to a fury, tearing at the lighthouse, which stood 100 metres high. In a hurricane, a ship must seek shelter for fear of being driven by the wind on to the rocks of which the lighthouse warned.

Yet here they saw, calm as you like, a ship passing the lighthouse with its cabin lights visible, sounding its fog horn. Here we have a meteorological impossibility: a tremendous hurricane alongside windless conditions with fog. As soon as the three lighthouse keepers saw that ship, they knew they were doomed.

The day when the adjacent dimension drifted over Eilean Mor rock cannot be ascertained for certain. What may be certain is that when the electrical storm abated and the phenomenon dissipated, the three lighthousemen remained behind, as had earlier in maritime history the crew and passengers of the Marie Celeste and other vessels.