The Supreme Court will deliver a bombshell ruling today on whether another Scottish independence referendum can go ahead without Westminster's backing.
Nicola Sturgeon wants to hold a fresh vote next October after arguing that Holyrood now has a pro-independence majority made up of the SNP and Scottish Greens.
The Lord Advocate referred a prospective Bill to hold another referendum to the UK Supreme Court - to test if the Scottish Government had the legal power to see it through.
Currently, only Westminster has the power to legislate for a referendum. All recent Tory Prime Ministers have repeatedly refused to grant another vote and the UK Government's position is independence is a settled question after the 2014 referendum.
Rishi Sunak has brushed off demands for another referendum but he has taken a less combative stance than his predecessor Liz Truss, who branded Ms Sturgeon an "attention seeker".
Here's what could happen after this morning's decision.
Court says Scottish Government CAN call a referendum
If the Supreme Court gives the plan the green light, the SNP and the Scottish Greens would join forces to pass a Bill for a vote on October 19 next year.
But the Scottish Government's case was this would provide for a "consultative" referendum, which means Ms Sturgeon would likely use the result to pile political pressure on Rishi Sunak to agree to another full-blown vote.
Legal expert Dr Andrew Tickell said the UK Government and other opponents would not be powerless to stop another referendum if the Supreme Court did rule this way.
"Even if the Scottish Government win this and have the opportunity to pass a piece of legislation through Holyrood, this isn't the end of the story," he told the PA news agency.
"Are (the UK Government) going to block it using their Commons majority? They could do that as a matter of law."
Dr Tickell added that the possibility of a boycott by opposition parties to any referendum - something Scottish Tory leader Douglas Ross has discussed but could be tricky for Scottish Labour.
Court rules against Scottish Government
If the court rules Holyrood cannot hold a referendum, hopes of a vote without Westminster's approval are scuppered.
The Scottish Government will be forced to continue pushing for a Section 30 order that would give the Scottish Parliament the power to call another vote.
Some independence supporters continue to call for an unofficial "wildcat" referendum, like in Catalonia, but Ms Sturgeon is reluctant to do so as the result could be seen as illegitimate.
Court refuses to rule on the referral
The court could decide not to rule on the referral because the Bill has not been passed by Holyrood - a key plank of the UK Government's argument.
Constitutional law Professor Adam Tomkins, a former Tory MSP, said he viewed this option as the most likely.
He said the Scottish Government could push ahead with the legislation and fight a Supreme Court challenge after its passage - but that would likely result in the resignation of the Lord Advocate, according to Prof Tomkins, which renders the approach the least likely.
The Scottish Government could also amend the ministerial code to say that in most circumstances, the Lord Advocate would have to deem the Bill within the competence of the Scottish Parliament, therefore allowing the legislation to be introduced.
Or the Scottish Government could pass the Bill to a high-ranking SNP member to introduce, given the less stringent legal requirements of members' bills.
Court rules referral not within powers of Lord Advocate but answers anyway
As was done with a legal challenge over abortion in Northern Ireland in 2017, the court could decide to answer the substantive question, while also accepting that the Lord Advocate did not have the powers to refer the draft Bill to the Court.
This would not be legally binding, but it would likely be treated as such.
