A nation is holding its breath, believing, much as they used to in another New Zealander, Graham Henry, that the impossible is possible: that a broken scrum can be repaired, a misfiring attack can be redirected and a defensive line tightened and quickened.
The All Blacks are obviously wary, knowing Gatland as they do, they sense he can nudge something extra out of Wales. All Black assistant coach Ian Foster is especially wary, having worked with Gatland for two years at the Chiefs, he knows his former assistant's methods.
Wales were Grand Slam winners this year, World Cup semi-finalists last year and it doesn't feel right they are in such a pickle. Foster, for one, isn't buying it.
"We have kept an eye on their last two games and they have not played as well as they would have wanted - obviously," he said. "But all that has done is highlighted that it is a game you have to turn up prepared for week in week out and quite frankly we have talked about us building through this tour for us and making sure that we prepare well because if you don't prepare well - if you don't do Sunday to Friday well - then you can get bitten on Saturday.
"We expect a very physical team. They carry hard, they like the breakdown and they like to play lots of phases, lots of continuity and they like to defend with a bit of linespeed. Knowing that, doesn't make it any easier [to play them]."
Wales lacked intensity in their previous two tests. Gatland should instil that. Wales lacked clarity in their game-plan: Gatland will simplify the strategy and remove ambiguity. Wales lacked a bit of passion and belief: Gatland's return will bring that as much like Henry he carries a respect and aura among the players that puts them on edge.
And if the prospect of all that doesn't keep the All Blacks focused, then Andrew Hore, a veteran of four previous clashes in Cardiff, can sound a warning.
"One of the last time's we were here we thought we had the game won and then Jimmy Cowan threw an intercept pass and they almost scored and got a draw."