Supposedly it is a mystery who the All Blacks see as their preferred midfield combination.
But if the answer hadn't necessarily presented itself in the build-up to this tournament, it probably has since the Rugby World Cup started.
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It's taken two weeks of action to confirm that the era of dominance enjoyed by rush defences is ending. It's not over, but like the last days of the Raj, it's obvious a new era is coming and the transition is going to take casualties.
The sweltering heat of Japan is killing those teams who build their game on their line speed and kicking. Ireland learned the hard way that what works in the icy rain of Dublin doesn't have the same impact in the humidity of Shizuoka.
Those teams who can't pass and catch under pressure to stretch and break a defence are in trouble. Those teams who seek contact, not space, are in trouble. Those teams who don't like to play with the ball are going to wish they did.
The two best performances so far have come from the All Blacks and Japan and they are tied by the common thread of high intensity, ball-in-hand rugby.
Invention has triumphed so far over conservatism, not always and not emphatically, but enough to see that it is the path of the righteous.
Perhaps that will all change in the knockout rounds, but the All Blacks aren't taking that bet.
This is a World Cup that will be won by those who use their imagination rather than those who try to restrict those with an imagination.
All of which means the All Blacks' best midfield is not quite a mystery on the Agatha Christie scale and certainly there is no need to call in Hercule Poirot to solve it.
The answer can be deduced by following the trail of evidence and connecting it to the All Blacks' motive to play fast and wide and trust their skillset.
It's surely been apparent to everyone that Anton Lienert-Brown is part of the deal. He's been on a different level all year regardless of whether he has played at second-five or centre, and form is everything at a World Cup.
He's bringing too much to be placed on the bench where he so often has been in the past and the real value of Lienert-Brown is his ability to be a midfield chameleon.
If the All Blacks need him to be direct and take it over the gainline, he can do that. He has footwork to wriggle into space, the best offloading game in New Zealand and the pace to stretch defences on the wider channels.
Whatever the All Blacks need him to be, he can be, and because he's so versatile, so difficult to pin as just one thing, it seemingly makes it harder to determine where best to play him and with whom.
Only seemingly because the answer has presented itself — Lienert-Brown at 12 and Jack Goodhue at centre is the combination that offers the All Blacks the best chance of playing with the width, speed and enterprise they so desire.
This is why the All Blacks have been so cautious with Goodhue since he damaged his hamstring in Perth seven weeks ago.
They need him at his best in this tournament and they need him to be purring come the knockout rounds.
Goodhue is in a different league as a distributor. It's his timing and appreciation of space that set him apart, along with his decision-making.
Several times at this World Cup, teams have found space on the outside channel, but too regularly, their centre has failed to capitalise — not run straight, or held on for too long.
Goodhue is the master at holding a defence-holding line that leaves space for his outside backs. He's also the master at knowing when to let the pass go and has been described by All Blacks coach Steve Hansen as the best exploiter of a two-on-one situation in New Zealand.
And that's what this World Cup is going to come down to for the All Blacks — ensuring every inch of space is effectively used.
If they are going to play this all-out attack game, it has to be well managed, held together by a calm head and visionary.
That's Goodhue — a young man wise beyond his years and capable of knowing that his role is to damage teams with his brain as much as his brawn.
He'll play maybe a half against Canada, and as Hansen said, it won't be about him proving that he can handle test rugby. That's long been done.
It will be about running some rugby into his legs, getting him ready for what lies ahead, so the coaches can reveal the answer to their midfield mystery.
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