When millionaire Harvard professor Arthur Kingsley Porter vanished without trace on a remote Donegal island almost 80 years ago, the rumour mill kicked into overdrive.
Had he accidentally fallen from a cliff or died by suicide? Had the 50-year-old been murdered? Or had he faked his own death and re-emerged with a new identity on mainland Europe?
A new book by Lucy Costigan explores Porter's remarkable life, shedding fresh light on the most likely fate of the renowned architect and author who moved to Donegal with his wife Lucy in search of peace.
The Co Waterford author was instantly gripped by the intrigue during a 2005 visit to Glenveagh Castle.
"There were just so many rumours. I wanted to find out more about the disappearance but also about him and his wife Lucy and to tell an honest story about their lives," she explained.
Her research led her to Harvard University, where she uncovered diaries and letters that provided insight into Porter's conflicted private life.
The son of a banking tycoon, Porter was born in Connecticut in 1883 and became an overnight millionaire when he turned 18.
He was 28 and a scholar of architecture when he met Lucy Byrant Wallace, seven years his senior, at a social gathering in New York.
He was shy, handsome, with a slender physique and a passion for the outdoors. She was a bright, dark-haired woman, exuding confidence and social grace.
The couple, who married the following year, shared a love of art, architecture and travel and spent much of the next decade travelling Europe.
"The letters from the early part of their relationship were very romantic. They had an incredibly deep and equal relationship and ached for each other when they were apart," said Costigan.
But Porter was concealing a deep secret. After 17 years of marriage, he finally confided in his wife that while he still loved her, he realised he was homosexual.
By then he was lecturing in the deeply homophobic environment of Harvard University, where the scandal of his sexuality would have destroyed his brilliant career.
Also by then, the couple had discovered Ireland, where they befriended the statesman and poet George (AE) Russell. In 1930, they purchased the remote Glenveagh Castle, a Victorian mansion on 30,000 acres, deep in the Derryveagh mountains in Co Donegal, for £5,000.
Porter also restored a fisherman's cottage on nearby Inishboffin Island. But their happiness in Ireland was short-lived.
Porter's recurring bouts of depression prompted him to seek help from Dr Havelock, an unorthodox psychotherapist and sexologist in London. He recommended that Porter give in to his desires with a young homosexual patient of his named Alan Campbell.
Incredibly, Lucy, whose adoration of her husband continued unabated, went along with the arrangement and Campbell became a regular visitor to Glenveagh Castle and to the Porter's home in Connecticut.
But depression set in again when Porter realised that his relationship with Campbell could not be sustained over time.
When the three set sail for Ireland on May 27, 1933, Campbell appeared to change his plans, travelling on to London instead.
Eleven days later, Porter went out walking during a storm on Inishboffin and was never seen again.
At the subsequent inquest – the first to be held in Ireland without a body – his widow recounted her frantic six-hour search with local fishermen.
"I think my husband must have slipped off the cliffs, fallen into the sea and been carried away," she said.
When she returned to Glenveagh, where the couple had arranged to meet AE, she told the author: "Kingsley will not return tonight, Kingsley will never return."
The inquest concluded that he had probably died from misadventure. But the coroner privately observed that Mrs Porter was "strangely without affect", as though her husband's disappearance was not unexpected.
A few years later, there were reported sightings of Porter in Europe and rumours of gay acquaintances.
In the wake of her loss, Porter's widow funded research to study the "nature, cause and treatment of homosexuality".
In 1937, Glenveagh Castle was bought by his former student, another millionaire, Henry McIlhenney. For a time, it became a playground for Hollywood stars such as Greta Garbo and Charlie Chaplin.
But the enduring mystery of the fate of Arthur Kingsley Porter has never been solved.
Lucy Costigan remains unconvinced that he met his death on Inishboffin that stormy day.
"When I was researching the book, I met a girl on Inishboffin island whose family was convinced he went off to Paris to start up a new life over there. Also, it came out at the inquest that one boat actually left the island that morning and for a decade or so afterwards there were sightings of him all over Europe and as far away as India, so there is still a mystery about it," she said.
Glenveagh Mystery, The Life, Work and Disappearance of Arthur Kingsley Porter is published by The Irish Academic Press. Work on a documentary and a film is also under way. Lucy Costigan is author of Strangest Genius, The Stained Glass of Harry Clarke.