An observant Jew who had fled horrendous persecution, Wartski found himself in conversation about the Bible's scriptures with the dog-cart driver who, when they parted, gave him his card and told him to make contact.
The card was for the estate of the fifth Marquess of Anglesey and the dog-cart driver was the Eton-educated Earl of Uxbridge, who was due to inherit the noble title, plus an income of £110,000 a year, today equivalent to around £11 million.
It was a fortune he was to squander in a madcap life, but not before he had set up Wartski in business with a jewellery shop in nearby High Street, Bangor, in 1865.
That provided Wartski with the launch pad to prosper, opening two more shops in neighbouring Llandudno. Their success allowed the formerly destitute Wartski family to enjoy the luxury of a chauffeur-driven Rolls Royce Silver Ghost and to employ two maids.
"The incurably rich fifth Marquess is pivotal to the Wartski story and to be there in north Wales at the heart of where it all began was both unexpected and exciting," Munn says. "The last five years have been a heady combination of family history, of course, but also of incredible art objects, jewellery, royals, dukes, earls and duchesses, personalities from stage and screen that is difficult to believe.
"The archives have been rather scant because the shop in Llandudno had stock books but there was a flood in 1960 which destroyed them. That was heartbreaking.
"Putting it all together has almost been like a stained-glass window that has been shattered. Time, as T. S. Eliot said, is like shards left over that you have to gather up and glue back together and make some sense of it. And that's what I've done."
A vital link has been the entrepreneurial Snowman family, who arrived in London's East End some 30 years before the Wartskis and made their way up the ladder. Hampstead-born Emanuel Snowman married Wartski's daughter, Harriet, and brought the Llandudno businesses to London.
His great coup was a tiny shop initially in the Quadrant Arcade, off Regent Street, which had Queen Mary as a regular customer and received royal warrants. He also spent £100,000 in 1927 acquiring 80 items from the Soviet government's "treasure for transport" sale. These included nine celebrated jewelled eggs and gold encrusted boxes, the work of the Russian royal family's jeweller Carl Faberge.
This raised the name of Wartski to the top of the establishment tree, Munn discovering in his research that King George V had visited the tiny shop,
From his home in Redington Road, Hampstead, Snowman also played a significant role in the Jewish community as warden of Hampstead Synagogue, providing help for refugees from Nazi Germany, serving as an alderman on Hampstead Council and being elected Mayor in 1953, the Coronation year.
Invited to Buckingham Palace to meet the Queen on a Saturday, he explained that he could not accept the invitation because it was Shabbat. The Palace apologised and suggested an alternative date.
His son, Kenneth, who attended University College School and was a trained artist, followed in his father's footsteps, forsaking an art career - his uncle was the painter, Isaac Snowman - to join the business. He added to Faberge's acclaim with major exhibitions and appeared in a James Bond story - Ian Fleming was a close friend. The story was included in the 1983 film Octopussy, in which a Faberge egg is crucial to the plot.
With Munn - hired as a 19-year-old trainee - on board, he bought a then unattributed Faberge aquamarine-and-diamond brooch for his wife, Sallie, at a country auction which wasn't identified until after their deaths.
Their son, Nicholas, stepped in as chairman. A brilliant musician and arts administrator, he co-founded and managed the London Sinfonietta as well as co-founding, with Pierre Boulez, the Ensemble intercontemporain in Paris. He later took on the role of general manager of the Glyndebourne Festival Opera.
Wartski has continued to prosper under his chairmanship, making the Welsh gold wedding rings for Prince Charles and Camilla and for Prince William and Kate Middleton.
Although Nicholas no longer lives in Hampstead, the Snowman link remains with the publisher and poet Jeremy Robson, whose grandmother was Harriet Snowman and who, for safety reasons, was born in Llandudno during the Second World War.
There are other Snowman royal connections. Dr Jacob Snowman, Emanuel's brother, circumcised Prince Charles and other members of the royal family. Isaac Snowman, Emanuel's other brother, painted royal portraits.
Munn now sees himself "like some old sage sitting on the wall. Having been here for 40 years, I've seen enormous peaks and troughs of wealth and can remember when every shop here in Grafton Street was for rent and there was tumbleweed rolling down the road.
"It's been very important to keep quite grounded. I have been enormously lucky to meet fantastically interesting people and to see wonderful, wonderful things."
All are depicted in his sumptuously illustrated saga of the Wartski family and business.
But "what remains really important is to take the bus home at night and remember that there is another world out there".
