The answer - for trivia fans everywhere - is the nine of diamonds. But why should such a non-descript card come to have such a dire meaning? Like most Scottish myths and folklore, there are so many explanations - some plausible, some bizarre - that it becomes a case of sifting through the stories to uncover the truth.
A truly fanciful tale is found in a claim by W Gurney Bentham in his 1931 book Playing Cards: History of the Pack and Explanations of Its Many Secrets. Bentham says the card became the curse because the Scottish crown could afford to have only nine diamonds, not ten like other countries. An example of English humour, methinks!
There are other fairly unlikely suggestions but along the way there are clues. The card was first recorded in print as "The Curse of Scotland" in 1710 - remember the date. Many bridge and poker players swear it relates to a game called Pope Joan, in which the nine of diamonds is the Pope - the anti-Christ to Scots Presbyterians.
Other Scottish historians claim it has nothing to do with card playing and that in the 16th-century reign of Queen Mary nine diamonds were stolen from the crown of Scotland by an Edinburgh freebooter called George Campbell - another clue there. A tax was levied on the people of Scotland to pay for the missing gems. The tax was given the nomenclature "Curse of Scotland", as did the playing card.
Certainly Campbell's deed was to live on in playing-card circles. The nine of diamonds, instead of being known as the curse, was sometimes named after unpopular Scots of the day – and Campbell featured prominently. So too did Moll Hepburne, a name for Mary Queen of Scots after her unpopular marriage to the 4th Earl of Bothwell, and the Justice Clerk, after the widely unpopular Lord Justice Clerk Ormiston in the early 1800s.
By now you may have seen a pattern of time emerging - that of the early Jacobite rising in Scotland. Too early for the next explanation, that the Duke of Cumberland – "butcher" to the Scots - scrawled the words "no quarter" on the back of a nine of diamonds to instruct his men that all those who had survived the Battle of Culloden in 1746 were to be killed.
But there was one man living in those lawless times to whom the card applies perfectly. He was seen by many as a curse on the land, responsible for one of the most heinous acts ever committed in Scottish history. He was an aristocrat with the number nine linked with his family. He was very active in Scottish politics in the 17th century and died in 1707, three years before the first written record of the nine of diamonds as the "Curse of Scotland".
Step forward the ever-reviled Sir John Dalrymple, 1st Earl of Stair who, as Scottish Secretary, gave the orders for the infamous Massacre of Glencoe in 1692 in which the Campbells killed 38 members of the Macdonald of Glencoe clan as they slept.
Whether Stair wrote the orders on the back of a playing card is doubtful. What is known is that the Stair coat of arms contains nine "lozenges" and a striking similarity to the nine of diamonds. In those days there was a huge anti-Campbell sentiment in the west Highlands and it would have been natural to link the hapless rogue George Campbell with the card said to curse Scotland.
Ted Cowan, professor of Scottish History at Glasgow University, says, "It is the only really credible explanation I can come up with and the one regarded by most people as having any substance."
So when you next play a game of poker, bridge or blackjack, and a nine of diamonds is dealt your way – quickly discard or fold. You don't want to be cursed!
If you enjoyed reading this, you may want to read:
Massacre of Glencoe
Mary, Queen of Scots