Could the European Court stop Brexit?
Irony of ironies, is it possible that the European Court could block us from leaving the European Union?
If you are an ardent Brexiteer, stop before your blood pressure goes through the roof. If you are a passionate Remainer, stop before you crack open the French (not English of course) champagne.
What follows is an unlikely, a very unlikely turn of events. But it is not impossible that our decision to leave the European Union could end up being judged in the European Court in Luxembourg. Yes, that same court so despised by Eurosceptics could, in theory, fight to keep us in their clutches.
As my colleagues have reported, the government is already fighting a challenge in the courts, an effort to make ministers accept that Parliament, not the prime minister, must decide when to trigger Article 50 - that's the legal mechanism that begins the likely tortuous process of us actually leaving the EU.
Without going into the details, which you can read about here, the claimants are arguing that the PM has to get MPs' permission to go ahead with it. The government's lawyers claim that she is perfectly within her rights to do so under the ancient principles of the Royal Prerogative.
A senior government source says it seems to be "60-40" in their favour, with the judgement expected in the next week or so. But both sides are likely to appeal immediately to the Supreme Court for a further ruling, and it's here that things could get interesting.
Both the government and the claimants have assumed that the Article 50 process can't be stopped once it has started. But not all lawyers agree, with some even arguing that Article 50 could legally be stopped in its tracks.
Although that question is not a bone of contention in this particular case, it is possible that the Supreme Court judges think that it ought to be part of the arguments.
If they do? Well, that question is a point of European, not British, law.
And, of course, European laws are not decided in the grand building opposite Big Ben but, you guessed it, in the European Court in Luxembourg. That wouldn't just have huge consequences for the Article 50 court case, but for the whole tricky political dynamics of Brexit.
George Peretz QC explains the legalities here, including why it is not that likely that the Supreme Court will take what would be seen as a provocative action.
And politically, as well as legally, a referral to Luxemburg is not a good bet.
In these strange times, though, neither is it an outcome that can be totally dismissed, complete with the huge political consequences that it could provoke.
As they pulled a horrified face, one minister said to me: "Imagine if Luxemburg stops Brexit!"
As the government battles to hold its line, imagine indeed.