Behind the picture is an A-Z Map of London with a big red X on it. They find the current A-Z Map and overlay it, but the house on the map does not exist, the small four and a quarter inch square does not exist. They look through other past maps - no house.

They go there and the centre of the X is in the middle of a road - past maps place a man-hole cover very near to the centre of the X, now tarmacked over.

They go into the sewers, lo and behold there is a shaft going up to where the man-hole cover would be. They get a step ladder and examine all the bricks in the shaft.

They find a loose brick with a pouch of diamonds behind it. Uncut diamonds. They take them to Hatton Gardens jeweller and spread them before a venerable old jeweller.

He re-coils in horror and shouts at them to take the diamonds away - the jeweller will not be questioned about why.

Same with another jeweller.

They take the diamonds to a younger jeweller who does not react.

Then they tell the young woman about the reactions of the previous two jewellers and what did she make of that?

“There’s some old folklore, but these can’t be those diamonds - they’ve been found and stored away securely. Oh, but not all were recovered, hang on, I’ve an old book somewhere.” She goes to the back of the shop.

And doesn’t return. They decide to go out the back to see, no-one there at all. The back door is open wide. There’s the book.

They read the book at the pages open. Folklore, nothing more.

They take copies of the relevant pages of the book, close the backdoor, lock it with the key found in the lock and leave the shop.

There are three of them - Julie, Mike and James. The picture is Julie’s, her Dad had died and left her the painting, but not the mount or the frame, hence finding the map taped to the back of it. Mike is her brother, James is her brother-in-law, Mike’s husband. Mike was given other paintings, seemingly random. They look behind all Dad’s paintings, no more maps or documents.

They look at the paintings, all very jolly, all cartoonish, but all in oils, like Goya. Hedonism seemed to be a constant theme. Dad was a very successful accountant, lots of the rich and famous were his clients. He died peacefully surrounded by his family. Mum died a long time ago in a car accident before seat-belts were mandatory.

They Googled the young jeweller’s book’s contents and found nothing. Nor any particular jeweller’s folklore. They had photographed the book’s cover and found no trace of it for sale or in a museum.

Julie got an email from the Premium Bonds saying she’d just won about £2500. Mike got a promotion he was angling for. James had sold one of Dad’s paintings for £65,000.

The three jewellers that they’d visited had merged into one and had taken possession of the largest jewellers premises in Hatton Garden. They floated on the stock exchange and all employees were instant multi-millionaires.

Provenance? Where had they come from, these diamonds?

After a week of Googling uncut diamonds and folklore, they came up with this :

Uncut diamonds should be cut by an expert to find the original beauty, like a block of marble with a perfectly formed David inside.

How to find an expert diamond cutter who wouldn’t recoil at the sight of these ones? The only way was for each of them to learn how to cut the diamonds themselves.

So they did. It took a lot of money, which always seemed to be available to them. There was a training centre nearby.

The amalgamated jewellers of Hatton Garden started to buy up all the other jewellers in the area.

They’d counted the uncut diamonds, there were thirteen of them. Cut, they were probably worth millions and millions.

At the training centre were many visiting experts. Without giving the game away, they probed each one on diamond folklore. After two years they were ready to cut the diamonds and knew their provenance.

Through many co-incidences, they had a net worth of about 10 million pounds, they no longer needed to work.

There was no 100% secure place or safe that they could keep the diamonds, they didn’t want to entrust them to any one else. So Julie kept them at the back of her wardrobe in a specially made cubby hole. She checked they were still there, all thirteen of them, every morning, afternoon, evening and night.

The day came to cut them. Julie got them from the cubby hole and laid them in a row on the bench. All twelve of them. She, Mike and James didn’t notice the missing one.

They got to work. As soon as James started on the first one he had a heart attack and died right there in the workshop.

The diamonds remained uncut. When Julie and Mike got back from the hospital, they collected the eleven uncut diamonds, put them in the pouch and stored them back in the cubby hole.

The folklore seemed to go like this:

Forsuch was a king of great wealth in Mesopotamia, though only by legend. There are no physical remnants of his reign. Only stories.

Of course all three believed they were pure of heart, they had no criminal convictions after all.

On the day that James died, the big jeweller in Hatton Garden filed for bankruptcy. Leaving hundreds of employees penniless and out of work. Their millions all spent on trying to save the business.

Mike, Julie and James had no children to leave anything to.

Julie had Dad’s picture reframed with a map of her house behind it and hung it up on the wall. With an X to mark the cubby hole.