Boris Johnson's new deal will be tested when MPs hold a special Saturday sitting of the House of Commons.
Mr Johnson returned to London following dinner on Thursday evening in Brussels, skipping day two of the summit as he attempted to shore up support.
Any hope of an easy passage was dashed after the DUP rubbished the fresh agreement.
But as well as debating the new deal MPs will also try and amend the legislation.
So far they have unveiled three amendments to the deal.
But various groups are furiously drafting further changes they want to table.
The most significant, put forward by ex-Tory Oliver Letwin, would refuse to approve Boris Johnson's deal in final form tomorrow - instead waiting until it's passed through its last vote next week.
The cross-party amendment has support from Labour's Hilary Benn, Lib Dem leader Jo Swinson, Plaid Cymru's Liz Saville Roberts and the SNP's Stephen Gethins.
It is also backed by former chancellor Philip Hammond, ex Tories Dominic Grieve and David Gauke and Change UK's Anna Soubry.
The bid will lock in the so-called "Benn Act" which forces the PM to ask for an extension if there's no deal agreed tomorrow.
The MPs behind it are worried that the agreement will pass the Commons - but then the government could still take the UK out without a deal anyway.
That's because technically, we haven't actually left until MPs pass a series of other votes on the EU Withdrawal Bill next week.
Meanwhile, two SNP amendments will also call for a general election and revoking Article 50 to cancel Brexit - but it's unclear whether they will even get called.
Speaker John Bercow has the final say over what reaches the floor of the Commons.
Meanwhile a bid to use Saturday's historic session to secure a second referendum is currently on hold - with campaigners looking to next week instead.
Remain MPs had planned to tack on a bid to get a second bill.
Yesterday they changed the rules surrounding Saturday's sitting in order to leave open the possibility of both Letwin's amendment and one on a public vote.
But they continued with frantic discussions to try and gameplay the most effective time to bring forward the vote.
