On December 26, 1900 — Boxing Day — the lighthouse tender ship Hesperus steamed toward the remote Flannan Isles, 20 miles west of Scotland’s Outer Hebrides. Relief keeper Joseph Moore expected the usual handover at the lighthouse on Eilean Mòr. Instead, an unnerving silence greeted the crew. No flag flew. No one answered the horn.

Moore climbed the steep path alone. The entrance gate was closed but unlocked. Inside the lighthouse, everything looked disturbingly ordinary yet deeply wrong. The lamps were cleaned, trimmed, and ready for the night. The kitchen pots were washed. Two beds were unmade. The clocks had stopped. Only one set of oilskins hung by the door — two were missing.

The three keepers on duty had simply vanished: Principal Keeper James Ducat (43), First Assistant Thomas Marshall (28), and Occasional Keeper Donald McArthur (who was standing in for an ill colleague).

The first warning had come eleven days earlier. On the night of December 15, the passing steamer Archtor reported the powerful beacon was dark. Winter storms had delayed the relief boat, so the full mystery wasn’t uncovered until December 26.

Northern Lighthouse Board Superintendent Robert Muirhead, who knew the keepers personally, led the investigation. At the west landing stage — 110 feet (34 meters) above sea level — he found terrifying evidence: iron railings twisted like wire, a one-ton boulder displaced, and a lifebuoy ripped from its mountings. Muirhead concluded that a massive rogue wave had struck during the mid-December gale. Ducat and Marshall likely went down to secure equipment; McArthur, seeing trouble, rushed out without his oilskins to help and was swept away with them. No bodies were ever found.

The official report was straightforward: a tragic accident caused by the sea. Yet the orderly state of the lighthouse, the missing oilskins, and the rule that one man must always stay behind raised questions that refuse to die. Why did all three leave their posts? Could something more sinister — a fight, supernatural forces, or even abduction — have occurred?

For 125 years the Flannan Isles mystery has haunted Scotland and the world. It inspired books, the 2019 film The Vanishing, and countless theories. The automated lighthouse still stands on that lonely rock, a silent witness to three men who walked into the mist and never returned.