Is Spain on the brink of break-up?
It's just possible that this weekend, one of Europe's most important nations will start to break apart.
The people of Catalonia, the richest region of Spain, will be voting on Sunday in an election which may - and I repeat, may - set them on a path to independence.
Just like Scotland, you may think. Well, no, not really. First because the central government in Madrid is most unlikely to give its approval for the holding of a referendum on Catalan independence, and second because, if the opinion polls are right, there is in Catalonia, unlike in Scotland, a pro-independence majority.
And that's something new. Last September, on Catalonia's national day, huge crowds took to the streets of Barcelona - some estimates put the number as high as two million - to call for independence in an unprecedented demonstration of fury at what is seen here as Madrid's contemptuous, even insulting, attitude towards the people of this immensely proud nation.
In part, this nationalist fervour is a by-product of the European economic crisis. Catalans contribute substantially more to Madrid's coffers than they get back, and, they claim, are being asked to make far bigger financial sacrifices than the central government to meet the demands of Spain's creditors.
Last night, I stood in a magnificent square in the heart of old Barcelona, gazing up at an eternal flame flickering at the top of a soaring metal sculpture. It's a memorial to the Catalan fighters who died fighting to defend the city in 1714, against the besieging Spanish and French armies. Catalan nationalists will tell you that today, nearly 300 years later, they're still fighting for the same cause.
Like their Scottish nationalist equivalents, Catalan independence campaigners insist that their new nation would remain a member of the EU and would be a good neighbour to the country from which it had broken away.
One businessman here told me the relationship between Madrid and Barcelona is like a marriage that has irretrievably failed. But when I asked him if divorce is really the only answer, he replied that unfortunately one of the parties to the marriage is refusing to consider one. Madrid, he said, is simply unable to accept the reality of a partnership that has broken down.
The reason all this matters far beyond Spain's borders is that the Catalans are not the only Europeans itching to form their own independent state. Quite apart from those Scots who favour independence, what about the Corsicans of France, or the Padanians of northern Italy? They will all be watching closely on Sunday.
It's not as if the EU isn't facing enough troubles as it is. There's the new budget to be agreed, and of course there's still a very real prospect of more financial turbulence over Greece's debts and, yes, Spain's too.
The last thing the Spanish government wants is to be thrown into a major constitutional crisis following this weekend's election. Catalan leaders insist they're not spoiling for a fight, but they are insisting on being heard.
If the election results in a clear majority in the regional parliament for parties that favour either full independence or substantially enhanced autonomy - and that's what the opinion polls are suggesting - the Spanish prime minister, Mariano Rajoy, will be faced with a stark choice.
Either he starts negotiating with the Catalans to see how many of their demands he can meet, or he faces them down and dares them to do their worst.
Right across Europe, many of his fellow EU leaders will be watching anxiously to see which way he jumps.
I'll be on air tonight, Friday, from Barcelona, with an extended report looking ahead to the election and analysing the likely repercussions for the rest of the EU. I hope you'll be able to tune in, or catch up later via iPlayer.