It is hard to overstate the magnitude of what happened in Cabinet today - because the prime minister and her senior ministers concluded over a record-breaking seven-and-a-half hours that Brexit was too hard for them to deliver on their own and they would now seek to enlist Jeremy Corbyn and Labour in finding a solution.
"There was a very significant shift to a softer Brexit," said a senior minister.
"There is no turning back".
And there you have captured the magnitude of the risk the PM is taking.
First, she is hoping Corbyn will negotiate in good faith - which may well be the triumph of hope over experience since he can legitimately query why she didn't offer proper cross-party negotiations months ago.
That said, Labour's leader said tonight he was "pleased" the PM was now "prepared to reach out".
Second, May needs a majority of MPs to either vote for a compromise she agrees with Labour's leader, or - if that were not to happen - for them to choose a way forward from a series of options presented to them, which again runs counter to what has happened in all votes during the recent so-called Letwin process.
Third, all this has to happen by Saturday, so the prime minister can write to the president of the European Council requesting a Brexit delay until 22 May.
Fourth, if - as ministers expect (perhaps naively) - there is a majority of MPs for a Brexit deal involving continued membership of the Customs Union, and possibly too significant permanent alignment with the EU's rules, the prime minister has to pray that her own party does not tear itself apart.
For the avoidance of doubt,Tory Brexiters are tonight spitting tacks - with one saying what she had agreed with ministers proved she was "the worst prime minister in history".
And there is evidence when it comes to the nature of a Brexit acceptable to Tory MPs and Tory members, what the PM seems to be endorsing as a way through the morass could leave her and her ministers isolated and stranded within their party.
Fifth, if it works, her partners in Government - Northern Ireland's DUP - will go ballistic, because the consequence would be approval of the Withdrawal Agreement and the Northern Ireland backstop, which they regard as more toxic and radioactive than plutonium. And at that juncture, the Tory government would collapse.
Sixth, she needs to persuade the EU her approach will allow all necessary legislation to pass by 22 May, which means that any new coalition with Labour MPs has to be stable.
Seventh, she needs to persuade us, the people, it makes sense to start preparations for participating in EU parliamentary elections, including finding candidates, launching campaigns and so on, all in the hope those campaigns can be cancelled on 22 May, before voting actually starts (believe it or not, the Government thinks this will be a necessary condition laid down by the EU).
So given the sheer number of conditions that need to be met for the Cabinet's agreement to succeed, I can find no MP outside of the payroll who think it will work.
Whether this plan works or not, a Rubicon of sorts has been crossed.
The prime minister and her ministers have signalled they are so opposed to a no-deal Brexit on 12 April that they will begin a process that could blow up the Tory Party. That matters and will have huge consequences - not least for how long she can remain prime minister.
PS According to ministers, defining issue was that if there was a no-deal Brexit "we’d have to go to direct rule in Northern Ireland," says one.
"Disaster. Huge risk. Of all legacies, the break-up of the Union [of the UK], the worst for a PM. She’ll never do no deal now."
And I am told: "Andrea [Leadsom] requested that we go ahead with the risk of direct rule but call it something else."