In just four days, Southampton are due to walk out at Wembley to take on Hull City in the richest game in world football - the Championship play-off final.

But the fate of the match is in the hands of an English Football League independent disciplinary commission.

As the club's supporters, players and staff woke up on Tuesday morning, there was no guarantee that the game would happen.

Instead, Tuesday is D-Day for the captivating Spygate story.

Saints stand charged by the EFL with watching a Middlesbrough training session two days before the first leg of their play-off semi-final.

Boro want Saints to be thrown out of the play-offs, arguing that spying on their preparation "goes to the heart of sporting integrity and fair competition".

If Southampton are found guilty - and they have not issued any kind of denial - then all options are on the table for the independent disciplinary commission.

The hearing began at 09:00 BST and a decision is expected later on Tuesday, but there is the chance it could drag on into Wednesday. It all comes down to how much time is needed for deliberations.

No-one can predict how this will end.

It was the morning of Thursday, 7 May.

Middlesbrough were at their Rockliffe Park training base preparing for the game against Southampton 48 hours later.

The supposed spy, allegedly a Southampton analyst, is said to have parked at the golf club, then walked a couple of hundred yards down a road which leads to a raised area of ground.

Sources told the BBC that the accused simply stood pointing his mobile at the training session, while wearing in-ear headphones.

Middlesbrough staff believe he may have been live-streaming the session via a video call.

A member of Middlesbrough's staff approached, say BBC sources, but the person would not identify himself. Then, he quickly deleted some content off his phone before running off into the golf club.

He jogged into the toilets, changed his clothes and hurriedly left the site.

Middlesbrough's photographer took photos and matched him to a photo on the Southampton website. One of those pictures was subsequently made public last week.

Boro were furious and quickly reported it to the EFL.

Within 24 hours the EFL had charged Southampton with breaking two regulations.

EFL Regulation 3.4, which requires clubs to act towards each other with the utmost good faith; and

EFL Regulation 127, which prohibits any club from observing, or attempting to observe, another club's training session within 72 hours of a scheduled match between the two clubs.

The independent disciplinary commission has three people, with the chair usually being a King's Counsel (KC). They sit with two side members who are lawyers, barristers or mediators.

It is expected to be a virtual hearing but it could take up to 24 hours for the verdict to be made public.

If guilty, options open to the independent disciplinary commission include a fine, a points deduction for next season or throwing Saints out of the play-offs.

Unlike, say, a profit and sustainability hearing, there is no framework or sliding scale of offence-to-sanction. This is completely new.

There is no direct precedent because no one has ever broken regulation 127.

The independent disciplinary commission will, in effect, be creating it - which adds further significance.

Whether spying is deemed enough for the panel to think it has a significant consequence over promotion will be key.

We have seen a spying case before, when Leeds United were found guilty of watching Derby training seven years ago.

Leeds were fined £200,000 but there are a couple of crucial differences.

Firstly, in 2019 there was no rule which outlawed watching the opposition train before a game. As a result, the EFL brought in regulation 127.

Then there is the timing. Leeds boss Marcelo Bielsa was caught sending a member of his staff to Derby's training ground in the middle of January, hardly a crucial point of the season.

Saints stand accused of spying on their opponents before one of the most important games of the season, a play-off semi-final.

The argument is that a fine would be meaningless if Southampton beat Hull to earn promotion to the Premier League.

That would give the Saints a minimum £110m in broadcasting revenues.

Another option is a points penalty. This could be seen as a halfway house, whereby the independent disciplinary commission dodges the nuclear option of banishing Southampton from the play-offs but still applies a sporting sanction.

If Saints get promoted, the EFL would not be able to unilaterally apply the penalty in the top flight, but it can recommend to the Premier League board that the deduction is carried over.

Removing Southampton from the play-offs would most likely be achieved by giving Boro a default 3-0 win for the first leg, and therefore a 4-2 aggregate victory.

The independent disciplinary commission must find a punishment which is fair but also acts as a deterrent to any other club who might try to spy - especially before a game of such magnitude.

Saints head coach Tonda Eckert and his staff could also face Football Association disciplinary action, though the EFL process must conclude first.

The coaching staff do have questions to answer.

Who knew what, and when? Was there a live stream? Was it uploaded anywhere?

At the 2024 Olympics women's tournament, Canada were found guilty of spying on New Zealand using a drone.

Fifa docked six points from Canada while three members of the coaching staff, including the head coach, were banned from all football for a year.

Most of the attention around Middlesbrough's statement on Friday centred on the club wanting Southampton thrown out of the play-offs.

But buried in the detail is one important fact: the Riverside club have not been named by the independent disciplinary commission as an "interested party".

This could turn out to be very important.

Firstly, Boro cannot attend Tuesday's hearing. Their evidence will be presented, but they will have no legal representation to argue their case.

This has angered Boro, who say that they are "directly affected by the matters under consideration and hold relevant factual evidence".

If the final outcome is not to Boro's liking - so any result which means Saints play Hull on Saturday - they have no right to appeal or challenge it.

Only the EFL or Southampton can appeal, which would be heard by an Independent League Arbitration panel with three new members.

An appeal should be held within 14 days, but the EFL is expected to ask for a resolution by Friday.

As Middlesbrough cannot appeal, they would have to take up a fight for compensation against Southampton.

In 2021, Boro launched legal proceedings against Derby County. They claimed the Rams' financial breaches had cost them a play-off place in 2018-19.

The two parties eventually reached a "resolution", which BBC Sport believes resulted in Boro being paid £2m.

Tickets eventually went on sale on Friday after an initial delay - but with caveats that the game could have different teams or be on another date.

If Southampton remain in the final, then the game is expected to go ahead as planned on Saturday.

But if Saints are removed, BBC Sport understands that the game is likely to be moved.

As Hull are preparing to take on Southampton, it would be unfair to give them just 72 hours to rip up their plans and start again for a game against Middlesbrough.

Boro would need to sell their ticket allocation, too.

And there would be the matter of the potential appeal by Saints, which would surely follow.

Wembley is booked up the weekend of 30-31 May, which is also when the domestic football season has to end.

So a rearranged game, if at Wembley, would need to be midweek - perhaps next Wednesday. To take place the following weekend, the EFL would need to find a new venue.

The EFL says that it makes contingency plans for all of its matches at Wembley, so alternative arrangements had already been sketched out before Spygate emerged.

Other than a statement issued by CEO Phil Parsons on 12 May, Southampton have kept tight-lipped.

Parsons said that the club would be "undertaking an internal review to ensure that all facts and context are properly understood".

Eckert has not been so fortunate to avoid the limelight.

The German has had to face news conferences and interviews around the two legs of the semi-final against Boro.

Both Eckert and the club's media team have attempted to shut down questions.

At one stage Eckert was asked by a journalist "are you a cheat?" - after which he walked out.

In a later interview with the BBC, he said: "I will say something, just not now."

"If we hadn't caught that man that they sent up five hours to drive, you would sit there and say well done [to Southampton] in the tactical aspect of the game and I would go home and feel like I've failed," Boro boss Kim Hellberg said after the 2-1 second-leg defeat at St Mary's.

"When that is taken away from you - 'we're not going to watch every game, we're going to send someone instead and film the sessions and hope they don't get caught' - it breaks my heart in terms of all the things I believe in."

Hellberg and Boro are unequivocal in their belief that they should walk out at Wembley on Saturday.

Usually, Boro's players would have jetted off on holiday.

Instead, they have had to remain in the north-east and on Thursday met at Rockliffe Park for a squad meeting. They were given a few days off but training resumed this week - for now.

Boro owner Steve Gibson has engaged the services of Nick de Marco, the sports lawyer with a record of delivering results against the game's governing bodies.

De Marco was recently heavily involved in making sure Sheffield Wednesday would start next season on zero points, when it seemed certain they would get a 15-point deduction.

But as Boro have not been named as an "interested party", that limits how much De Marco can influence proceedings.

Boro believe Saints may have spied on other Championship clubs this season, though it is unclear how admissible this allegation would be.

Hull City are also massively affected by all this.

Sporting director Jared Dublin told BBC Sport last week that the Tigers would be "preparing to play Southampton until we're told otherwise".

But Dublin feels Hull have become "collateral damage" in a case which does not even involve them.

Their supporters' groups agree, issuing a joint statement saying the EFL should "get their priorities right and put fans over function", external.

The game must take place on Saturday, they say. Fans stand to lose money on transport and accommodation if it is moved.

In this case at least, there was little more the EFL could do.

Southampton were charged within 24 hours of the complaint being raised, and from that point on the process and timing is controlled by the independent disciplinary commission.

If Saints are removed at such short notice it creates a catalogue of logistical hurdles.

Hull can only carry on as though everything is normal.

The coaching staff are specifically conducting training with the idea of playing Saints, while also trying to stop the players from becoming distracted by the conjecture around the fixture.

City plan to travel down to London on Thursday to continue their preparations.

But depending on the outcome of the hearing, they might have to rip those plans up and start again.

This is a mess not of Hull's making, yet they are fully embroiled in it.

At least it should all be over very soon, one way or the other.