Like all the most romantic treasure hunts, it began with a serendipitous encounter. But idle chat among old sailors and Titanic enthusiasts has spiralled into a search for gold thought forever lost in Scottish waters.
So, in June, an international group of salvage operators will begin scouring the bed of the river Tay in search of 60 ships and more than £2bn worth of plundered wealth. If they succeed it will be a remarkable maritime tale - all down to casual chat and local folklore.
Late last year, the Dundee branch of the charity Maritime Volunteer Services decided to mark this April's 90th anniversary of the sinking of the Titanic liner with an exhibition and thereby also raise much needed funds.
While organising the exhibition, they came across Gary Allsopp, the chief executive of Subsea Explorer, a company that takes tiny submarines 12,000ft down to the wrecked Titanic.
"We got talking to Gary about salvage and, because we know the river, we told him about how George Monck's fleet went down in the Tay," said Brian Callison of MVS. "It's always been a part of local folklore, but we said it would be great if someone came to look for it." That conversation began a historical search reaching back 350 years, and laid the seeds for the £1m salvage operation Mr Allsopp is organising.
The history is remarkable. In 1651, George Monck, general of a Puritan army of 7,000 men, sacked the city of Dundee. It was an astonishing feat: at that time the walled city was considered among the safest in Britain.
But Monck was determined. Many Scots noblemen were royalists and Cromwell wanted revenge. More than that, Dundee was known to contain the wealth of the viscount of Newburgh and the earls of Tweeddale and Buccleuch - not to mention Edinburgh's gold.
Getting behind Dundee's walls was not easy so Monck engaged a young man as a spy. Through him, he discovered that the army within the city regularly got drunk in the morning. David Kett, of Dundee libraries, says: "They had a liquid breakfast which carried on until lunchtime."
The information gave Monck the chance he needed. He launched a brutal attack on the city: 5000 people were killed as his men raped, pillaged and plundered.
"Blood flowed in the streets, that's well documented," says Mr Kett. "Monck only called off the attack after he saw a young baby trying to suckle on his dead mother's breast."
At the end of the attack, Monck decided to take his loot back to Leith. From Dundee's harbour he took more than 60 ships, ranging from 10 tons to 100 tons, and they all set sail early in September 1651.
They did not get far. In a contemporary account, Monck's chaplain, Dr Gumble, wrote: "The ships were cast away within sight of the town, the great wealth perished without an extraordinary storm."
It is thought that the 60 ships, crowded together, hit one of the Tay's notorious sandbanks, or perished trying to take an impossible route.
The sinking so close to Dundee must have been heart-breaking for Monck. But it is enormously fortuitous for the salvagers. The wrecks are thought to be buried deep in the sand, three miles south-east of Budden Ness.
"We are pretty confident we know where the ships are," says Mr Allsopp. "We know the movement of the sandbar over 350 years and we feel we can pinpoint it. It is highly unlikely they would have been washed out to sea."
The hunt has only limited time. The salvagers hope to get the operation under way in June and completed within 10 weeks. Although the waters of the Tay are quite shallow, the swells are large outside the summer months and the work, even within this movement, is dangerous.
But the spoils are great. The ships sank with £2.5m of Scottish coins - each one of these is worth £10,000 today - and other items belonging to wealthy Scottish gentry, which have been listed only as gold, silver, jewels, and rings.
Although the salvage belongs to the crown, the salvagers will be eligible for a reward for their find.
Their success or failure will be watched by an international audience: it will be broadcast live on the internet.
"Mr Allsopp says: " There are enormous problems to be surmounted. I'm sure we can overcome them. It's a really romantic adventure and I'm glad to be a part of it."