Wales versus England, the Championship decider, any sort of win for England and they are Grand Slam Champions, an eight point win for Wales and they retain the Six Nations, even seven points will do it if they maintain their superior try count, a Wales win by less than seven though and England still win the Championship.
It is a huge game, just about as big as it gets in terms of Northern Hemisphere rugby; it is a game that needs no extra spice added.
Yet there is extra spice added, and a lot of it. This game will play a huge part in decided the make up of Warren Gatlandâ€™s Lions squad, maybe even his Test XV. As we have written elsewhere, the ability to perform under the kind of pressure that the players will experience on Saturday in exactly the kind of ability that will be required out in Australia where the pressure will be extreme.
Within that though there will be a number of key battles between players, some who may already both be pencilled in but are fighting for pole position in the race for a Test jersey, some who are maybe fighting for just a seat on the plane.
It is tempting to just go through the sides 1-15, such is the ferocity of competition for places however we have narrowed it down to five key battles (with a bit of cheating!).
Scrum Half â€“ Mike Phillips v Ben Youngs
It seems likely at the moment that these two very different scrum halves will tour. Danny Care, Connor Murray and Greig Laidlaw all have their backers and one of those three will likely go too, but in the battle for the Test shirt it would seem that these two are the frontrunners.
Phillipsâ€™ aggressive and all action style was perfect in â€™09 in South Africa but a dip in form over the Autumn and in the early rounds of the Six Nations saw him falling down the pecking order, an upsurge in form and fitness lately sees him back in the reckoning though.
Youngs has had his ups and downs too but his controlled tactical game reading of the game has seen him firmly established as Stuart Lancasterâ€™s number one number nine.
Whichever of these two can exert a greater influence on matters on Saturday will be making a big statement to Warren Gatland about where that number nine shirt should be heading.
Hooker â€“ Richard Hibbard v Tom Youngs
Hibbard and Youngs have both fairly firmly established themselves as their nations first choice hookers, the challenge now for them is to force their way onto that Lions plane.
With Rory Best the only hooker to have really nailed down a seat on the plane there are still probably two slots left for hookers and it is perfectly conceivable that both of these players could tour.
They will face competition though, from within their own camps, and from the likes of Richardt Strauss, Ross Ford and Sean Cronin outside.
First and foremost they both have to hit their lineout targets, something Youngs in particular has struggled with, but from there if they can produce an impressive performance they may well book themselves a seat in what is a very open position.
Prop â€“ Joe Marler & Dan Cole v Gethin Jenkins & Adam Jones
This was a tricky area to decide on, is it key individual battles, is it a collective battle, are they all in with a shout?
The truth is though that it was impossible to separate all of those strands. Most interesting to me is who will perform best, Dan Cole or Adam Jones? Both are certain to tour and will be the main contenders for the tighthead shirt, they both offer a tremendous amount in both the loose and the scrum, Cole probably edges the loose and Jones the scrum, it is very close though. How they perform on Saturday will resonate with Gatland.
For Gethin Jenkins Saturday is huge on several fronts, for a start he is captaining the side, how he handles that may prove important. He will also be keen to prove that his return to form is permanent; Cian Healy is currently above him in the pecking order so Jenkins needs to put in a big performance. There are still some lingering doubts about his scrummaging too so a strong outing against Cole will be credit in the bank.
Assuming that Gatland takes three looseheadâ€™s then including Healy and Jenkins, Marler is very much in with a shout. Englandâ€™s other looseheadâ€™s, Alex Corbisiero (when fit) and Mako Vunipola are also in with a shout but while Marler is the man in possession he is the man with the best chance, if he can prove himself against Jones then Gatland can be sure that he can handle whatever the Australians have â€“ can he handle the pressure though? Needs a big game to elevate himself above Ryan Grant and Paul James.
Centres â€“ Roberts & Davies v Barritt & Tuilagi
I would expect that three of this group of four centres will tour, along with Irelandâ€™s Brian Oâ€™Driscoll. It is possible that Gatland may take just two fly halves to give himself a fifth centre option but it seems likely that he will take three, with one able to play in the centres, leaving just three spots for these four centres.
Barritt and Tuilagi have probably had the edge over Roberts and Davies so far this tournament but the Welsh duo are on an upward trajectory since the start of the tournament, albeit not with the steepest of inclines.
A year ago I would have said that Roberts was a definite tourist with Davies and Tuilagi also pushing very hard, Barritt was barely in the equation. Now Tuilagi seems a certainty and the case for Barritt is incredibly strong, he is Englandâ€™s defensive lynchpin and the glue in their backline.
With Andy Farrell going as defence coach you can be sure that he will be pressing the case for Barrittâ€™s inclusion very hard and he looks like he could tour now. Roberts meanwhile has looked out of sorts and now looks the most likely of the four to miss out, he does a lot of the dirty work but the spark seems to be missing from him at the moment.
Davies has improved since his howler against Ireland in the opening week but is not back to his 2012 form yet, he needs a big game tomorrow to cement his place.
If either set of centres can get on top and make a big impact on Saturday they will give themselves a huge boost in terms of Lions selection. It will also be a key area of the game, if either side finds themselves shackled in midfield it will be hard to win.
Openside Flanker â€“ Robshaw v Warburton v Tipuric
Ok, Warburton is playing at six with Tipuric at seven but the point remains; this game is huge for both Robshaw and Warburton for a variety of reasons.
Let me deal with Tipuric first though, a strong outing here and he can force his way onto the plane, as the most natural openside competing for the Home Nations if he can get on top in a game as big as this then his case will be hard to ignore.
Robshaw v Warburton is interesting though because of the captaincy issue too. In my view Warburtonâ€™s shot at captaincy is all but gone, with Wales passing over the captaincy to Gethin Jenkins for this game it seems impossible not to read it as an admission that Warburton may not be able to handle the pressure of captaincy and maintaining his own form in a game of this magnitude, if not in a Championship decider then could he really handle it under the pressure of a Lions tour?
It is key for Robshawâ€™s captaincy claims too, for two reasons; first he needs to show that his ability to make key decisions under pressure has improved since the autumn. I believe it has but he needs to demonstrate it because there is no room for indecisiveness in the heat of the Lions battle.
Second, he needs to get on top of the Welsh back row, if Robshaw is outplayed as a seven by Tipuric or on the floor by Warburton then it becomes very difficult to make him the Lions captain because there a two guys there who outperformed him, his performance is key.
Whichever of these three players can take this game by the scruff of the neck and turn it their way, will have put themselves right at the top of the pile for selection at openside, and could go a long way to deciding the destiny of the captaincy.
Keep an eye onâ€¦
Alun Wyn Jones, heâ€™s looked good since his return to fitness, a big game here against the form second row pairing could seal his place on tour, he has got catching up to do after missing the first few games but he is catching up fast.
Tom Croft, Croft starts his first international for a year after breaking his neck. His comeback has been remarkable so far and a big game here could see him sneak his way into Gatlandâ€™s plans. A world class performer at his best.
Owen Farrell, pretty much assured to tour, but this is the biggest game in Farrellâ€™s career. He has a reputation for being ice cool under pressure, this will be the biggest test to that he has ever faced, pass it and he could become very, very important in Australia.
Alex Cuthbert, at this stage George North is probably the only winger guaranteed to tour, with Tommy Bowe a guarantee if he can get fit and get some games. Cuthbert then is in with a real chance but he will need to perform tomorrow. Chris Ashton could also have a shot at the right wing berth but he has a lot of catching up to do on current form.
Worth a lookâ€¦
The coaching battle, the defensive masterminds of these two sides, former Wigan Rugby League stars, Shaun Edwards (Wales) and Andy Farrell (England) will both be geared up to prove their credentials.
Farrell has been chosen by Warren Gatland for his Lions coaching staff ahead of Edwards, Edwards will want to prove that he is the top dog while Farrell will want to show that Gatland made the right call.
The last wordâ€¦
While this is an important game Lions wise, the real focus tomorrow is on the Championship and its destination. Choosing a favourite is a near impossible task, the form book and the stats suggest it is simply too close to call.
I expect England to win the Championship, whether they can win the Grand Slam or not, I could not say, I would expect a very narrow margin either way though.