The pressure on the prime minister to work on - and disclose - a plan B, as a contingency against the expected rejection by MPs of her painfully negotiated Brexit plan, is building relentlessly and remorselessly.
She does not wish to do that, because she fears it would make it far easier for her MPs to vote against her on December 11, because they would know their votes were conscience-salving protest votes, rather than deal-destroying and possibly government-wrecking extreme sabotage.
But as the resignation of her thoughtful and phlegmatic universities minister, Sam Gyimah, shows, if she does not show leadership in pointing towards an alternative and plausible route to Brexit, there is now a high risk she will completely lose control of events.
He is not attached to the People's Vote campaign in any formal way. But he is one of a growing number of MPs from all parties who have come to the view that the UK’s March 29 date of exit from the EU should be postponed, so that the British people have the opportunity, now that they know more about the realities of leaving the EU, to decide whether Brexit is still what they want.
The risk for May is that if she is incapable of advancing a credible alternative path to Brexit, that infamous and elusive plan B, then Parliament will take the decision out of her hands.
The longer she says that her deal is the only deal, the longer all MPs - including her own, like Gyimah - have to formulate counter-proposals. And the position around which backbench MPs may coalesce is increasingly likely to be one she says she hates - such as another plebiscite.
What is no longer working, as a threat to coral MPs into line, is the idea that the rejection of her plan will lead to a no-deal Brexit. Too many MPs are so set against that outcome - at least if it were to look about to happen without a much longer period to prepare for and mitigate the shock - that they will find a way to block it, including in extremis ejecting her from Downing Street and even the government from office.
When the Japanese PM publicly calls on May for “support to avoid no deal” - as he did today here in Argentina - because of the damage trade friction at the border would do to important Japanese companies with big factories in the UK, it is very hard for the PM to plausibly argue that she would simply let chaotic events drive the UK to the cliff edge of an unnegotiated withdrawal from the EU.
Which is pretty much why every one of her MPs is convinced she has a Plan B. And they will vote to reject her Brexit deal confident they are right about that.
So if May wants to avoid losing both Brexit deal and her job, it may be that she needs to stop being quite so coy about the path or paths she may take, if (when?) she loses in 10 days.