When author Christopher Marsh wrote a riddle into his novel he was certain it would never be solved. But now a Belfast reader has unlocked the complex code 18 months after the book, A Year In The Province, was published.

The exact co-ordinates of where a Spanish medieval coin was hidden were buried in a complicated set of clues scattered through the story of Jesus Sanchez Ventura, who swaps the orange groves of Andalucia for Orangemen of Belfast.

David McNeill and his wife Sheila recently made the trip to Rathlin Island where they found the ancient coin placed in a hole within an internal wall of the ruined house at Rue Point, the southernmost tip of the island.

Mr McNeill (47), who has represented the UK at the World Sudoku Championships, said he could not resist the puzzle.

“I read it over the summer; my wife read it first and suggested I might find it funny. It was quite humourous and quite outrageous in places, but it was really the riddle I was interested in,” he said.

He had a hunch the secret coin might be on Rathlin as the riddle hinted at geographical coordinates matching the area.

He used rhyme to deduce co-ordinates from the clues, such as ‘thrifty wife’ sounding like 55 and ‘Portaloo’ sounding like 42. He then used the coordinates to pinpoint the genuine 15th century Spanish coin’s location.

“The first bit of the riddle was ‘thrifty wife with clean Portaloo’, so we found that thrifty wife was 55, with clean was 15 — although at first we thought it was 16 – and Portaloo was 42. So that gave us the northern coordinates,” Mr McNeill explained.

They found the coin tucked behind a loose stone in the corner of the ruined building.

But the Belfast man does not want to keep it. “I think I am going to try to return it so maybe Mr Marsh could be inspired to write another book.”

Author Marsh, a history lecturer at Queen’s University Belfast, was amazed that the riddle had been solved.

“In order to crack it, they had to find their way through a forest of anagrams, rhymes, map coordinates and other cryptic verbal clues.

“Then they had to use a map or satnav to pinpoint the location — I think they did it with a map — and travel there in order to unravel the last parts of the riddle. They must have walked the three miles from the harbour, almost certainly in high winds. I'm amazed that anybody found the coin at all,” he said.

The McNeills must take it now to Conor Cafe in Belfast, where they can claim a fee meal for two “and a fine bottle of Bushmills that I had assumed I might end up drinking myself,” said Mr Marsh. Manus McCann of Conor Cafe said he agreed to provide the prize after speaking with the author about his book. Staff are now waiting for Mr McNeill to come in for his meal and drink. He is delighted to be giving away the vintage whiskey.

“I didn’t believe that it would be solved at all, the bottle of whiskey was almost getting in the way in the stock room. Hopefully he won’t be waiting as long to claim his meal as the bottle has been waiting here with us,” he said.

How reading between lines solved author’s Rathlin riddle

Author Christopher Marsh peppered his book with hints of where a medieval coin was hidden, including a riddle, which reads:

A coin stored ('twixt rhyme and reason)

Thrifty wife with clean Portaloo, licks the leaven of heaven, and upward points to a seam of red, with openings from one to seven.

(Where poacher and gamekeeper live as neighbours, they rarely do each other favours).

‘A coin stored' is an anagram of coordinates and ‘('twixt rhyme and reason')’ hints that in order to uncover the exact geographical location of the coin, the reader must find numbers which rhyme with the words.

Thrifty wife (55) with clean (15) Portaloo (42) Licks (6) the leaven (11) of heaven (11).

This gives the reader 55 degrees 15 minutes and 42 seconds north and six degrees 11 minutes and 11 seconds west.

The next two lines:‘Upward points to a seam of red, with openings from one to seven’, refer to a line of bricks in the corner of the ruined building where the the coin was placed in one of seven cavities.

The final lines describe buildings nearby. One building was associated with smugglers while the other was a headquarters for Customs men — hence ‘poacher' and ‘gamekeeper'.