Theresa May went to Brussels on Wednesday in order to seal a deal to take the UK a big step closer to quitting the European Union. Everyone thought it was a formality. It wasn't.
As it was confirmed there was no agreement on the Brexit 'divorce' settlement, here's where everyone stands after a day of high political drama:
What is the issue with the Irish border?
The Irish border - specifically the border between EU-member Ireland and the British region of Northern Ireland - is proving to be a major obstacle. Protracted talks over its future status is preventing negotiations between the UK government and the EU to start over a future trade agreement.
Dublin fears the creation of a 'hard border', replacing the existing 'soft' arrangement, could disrupt 20 years of delicate peace in Northern Ireland and put the Good Friday Agreement in jeopardy.
Some have alluded to the the army checkpoints and watchtowers that dotted the 310-mile border during the Troubles, andIreland has sought assurances that nothing similar will be revived.
However, there has been a stalemate.
Ireland has called on Theresa May to keep Northern Ireland in the EU's customs union - essentially a free trade area - in order to avoid the 'hard' border.
But, as the UK government is at pains to argue, this goes against the principles of Brexit, which it says must include the UK leaving both the customs union and the single market, which permits free movement of goods, people, services and capital.
That's enough of a catch-22 without the Democratic Unionist Party potentially bringing down the minority Conservative government.
Why is the Democratic Unionist Party (DUP) having an influence?
The Northern Irish DUP and its 10 MPs in Westminster has been propping up the Tories after signing a 'confidence and supply' agreement following May's disastrous snap General Election. Walking away from the deal is the Northern Irish party's trump card.
Last week, speculation mounted that a deal was being thrashed out to harmonise trading relations in some areas between Northern Ireland and the EU (or, in other words, the Irish republic). The DUP appeared willing play its hand, hinting that any deal to "placate Dublin and the EU" would mean the Conservatives "can't rely on our vote".
READ: Who Are The DUP? Meet The Northern Irish Political Party Propping Up The Tory Government
So how does the UK government satisfy both the north and south of Ireland?
With great difficulty.
On Monday, a leak of a draft text suggested the UK had agreed that Northern Ireland would maintain 'regulatory alignment' with the EU to prevent the need for customs checks at the border.
A 15-page joint statement from the European Commission and the UK stated that "in the absence of agreed solutions the UK will ensure that there continues to be continued regulatory alignment" with the internal market and customs union.
This is where confusion reigned supreme.
As the text was passed around Brussels, London, Dublin and Belfast, debate raged over whether 'regulatory alignment' constituted effectively still being an EU member. A former Treasury adviser did not think so:
As press conferences and lunches were arranged and cancelled as reports varied as to whether the DUP and the Irish government had agreed the deal, it was soon clear the unionists would not buy it.