MPs have returned to Westminster 19 days earlier than expected after the Supreme Court ruled that the suspension of Parliament was "unlawful".
Boris Johnson has repeatedly said the UK is leaving the EU on 31 October. However, should the PM fail to strike a Brexit deal by 19 October, a law passed by MPs says the PM must extend the deadline.
But could a no-deal Brexit still happen on 31 October?
So what exactly is this law and how might the government try to get round it?
Brexit extension law
What does the Brexit extension law say?
Before Parliament was suspended MPs passed a new law - introduced by Labour's Hilary Benn - designed to stop Boris Johnson pushing through a no-deal Brexit on 31 October.
In September MPs passed a new law - introduced by Labour's Hilary Benn - designed to stop Mr Johnson pushing through a no-deal Brexit on 31 October.
Under the law, MPs Mr Johnson is required to request a three-month Brexit delay by 19 October.
Under the "Benn Act", Mr Johnson would be required to request a three-month Brexit delay unless he can pass a deal or get MPs to approve a no-deal exit by 19 October.
But - as with everything in politics at the moment - it's not as simple as that.
However, despite the new law, International Trade Secretary Liz Truss insists Brexit will still happen at the end of the month:
There are two scenarios in which Mr Johnson would not have to request an extension:
"We'll leave without a deal. That's clear - deal or no deal, we're leaving on the 31st", she told the BBC.
In either of these scenarios, Mr Benn's law would not force any Brexit extension to be requested.
So what possible options might the government be looking at?
Could the government ignore the law?
Two letters
The law states that it is the prime minister himself who would have to request an extension directly to the president of the European Council.
The law would force the prime minister to request the extension via a letter - it even sets out the exact wording.
It even includes the exact wording of the letter.
One idea that has been floated is for Mr Johnson to follow the rules but write a second letter, telling EU countries that he actually does not want an extension.
So, theoretically, Mr Johnson could refuse to write or sign that letter. But that would almost certainly lead to more court action.
This could lead EU countries to decide not to grant the extension as it would be clear it is not what the UK government actually wants.
There have been suggestions that Mr Johnson could follow the law by sending the letter - but send another letter setting out his political policy to leave on 31 October.
In this scenario it is possible the EU could simply ignore the second letter and just grant the extension.
Could the government override it?
Persuade someone to reject
Former Conservative Prime Minister John Major has suggested Mr Johnson could consider an "order of council" to override the Benn Act. Normally, this power is used by ministers to update the rules and regulations of public bodies, such as the General Medical Council. An order of council does not require the consent of Parliament or the Queen.
Any extension to the Brexit deadline would have to be agreed to by all EU member states. So, theoretically, Mr Johnson could comply with the law by writing the letter, but persuade just one country to veto it.
But attempting to use an order of council to override the Benn Act would lead to uncharted legal territory - so it's unclear whether it would even be allowed. Plus there's no suggestion from the government that such an option is being considered.
But persuading a country to side with the departing UK over their European neighbours could be a long shot.
It is only a request
MPs vote for no deal or reject an EU extension
Even if Mr Johnson agrees to write the letter, it would still have to be accepted by all of the other EU governments.
The prime minister would avoid having to send any letter if MPs vote in favour of a no-deal Brexit by 19 October. This is almost impossible as there is no majority in Parliament for this.
It is possible that other European leaders are not convinced that they should grant the UK another delay - particularly if they think the extra time is not used for the right purpose.
In another scenario, the EU grants an extension but proposes a date other than 31 January 2020. If that happens, MPs would have the power to reject the proposal, therefore leaving us heading towards a no-deal exit.
If the EU agrees to an extension but to a date other than 31 January 2020, the UK would need to agree to this, unless MPs vote against the proposal.
Ignore the law and wait for the courts
In this unlikely scenario - MPs rejecting an alternative extension - the UK could be left on course towards a no-deal Brexit on 31 October.
The most simple option for the prime minister is to sit on his hands and refuse to write a letter. This would almost certainly lead to legal action and constitutional experts have suggested he would face almost certain defeat.
What about an election?
Mr Johnson could bank on the legal process taking over 12 days to complete, which would take him past the Brexit deadline before being forced to ask for an extension,
Some MPs believe the only way to ensure a no-deal Brexit is avoided is to get a new prime minister.
Refuse to resign
Normally, the easiest way to do this is through a general election.
One option open to MPs who oppose a no-deal Brexit is to defeat the government in a vote of no confidence. In this scenario, an alternative government could emerge and take over from Mr Johnson if it can prove it has the confidence of a majority of MPs.
But Parliament rejected Mr Johnson's offer of an early election on two occasions. The MPs that voted against the against were worried the PM would move the day of the election to after 31 October, forcing a no-deal Brexit in the process.
By convention, Mr Johnson would visit the Queen to resign and recommend the appointment of whoever the leader of the alternative government is.
It is now too late to hold an election before the 31 October, because it takes at least 5 weeks to prepare one. But the government has indicated it may ask MPs for their approval again soon.
In theory, he could refuse to leave and become a squatter behind the black door of No 10. This could put the Queen in an unprecedented position as she may be forced to sack him.
One suggestion from Attorney General Geoffrey Cox was to pass a one-line bill in order to set the day of an election in stone before 31 October. But this would require MPs to change the rules on how elections are called and organised.
An alternative government?
If the Labour Party does not want to agree to an election before a no-deal Brexit is off the table, there is still another option: a so-called "government of national unity".
If Parliament was to back a vote of no confidence in the government, MPs would have 14 days to try and form a government that has the support of a Commons majority.
This could be a cross-party collection of MPs committed to blocking a no-deal Brexit. Theoretically, a new government could form for the sole purpose of requesting an extension to Brexit, before triggering an election.
The main obstacle here is party politics: Labour doesn't want to support any government that does not have Jeremy Corbyn at its head. However, the Liberal Democrats' leader, Jo Swinson, has said her party won't support a government that has Mr Corbyn at its head.
Could no deal happen in the future?
Remember, the options open to MPs to force an extension aim to avoid a no-deal Brexit on 31 October, but they can't rule out a no-deal Brexit in the future.
There are only two ways to do that: pass and implement a withdrawal deal or cancel Brexit altogether.
