You turn your back for five minutes and they go and change the Secretary of State for Scotland.
With all eyes on the Conservative side of the Coalition no one was expecting a flanker from Nick Clegg, and with the Scottish referendum a year from shore no one expected him to drop the pilot.
Michael Moore has been steady on the bridge at the Scotland Office during one of biggest political storms Scotland has ever seen.
Faced with the election of a majority SNP government, the prospect of an independence referendum at a time of Alex Salmond's choosing, the Borders MP found himself at the forefront of the battle to save the Union.
In the middle of it he found time to deliver the Scotland Act, which will give more powers, including tax raising, to Holyrood in 2016. That would be an achievement in itself.
More importantly he negotiated the Edinburgh Agreement for the Scottish referendum, in short time and within the red lines that Westminster needed to win - one question, before the end of 2014.
Though appointed accidentally, when Danny Alexander had to move to fill David Laws' shoes, Moore turned out to be the just the right man for the job.
Reasonable, amiable, ponderous - it was hard for the SNP to get angry or fall out with Moore. With their own consultation showing them what Moore was suggesting, one question, and the support base
demanding that a referendum not be missed, Nicola Sturgeon decided to do business and settle the terms.
I always thought the winner in the independence debate was going to be the side that sounded most reasonable. That is why the combination of Moore and Alistair Darling as leader of Better Together made sense. Neither are passionate politicians but they do sound reassuring.
So the Scotland Office half-time substitution marks a step change in Westminster approach to the referendum campaign.
Moore's replacement, Alistair Carmichael, is a different kettle of fish. A far more combative and self-assured performer he will be easier for the equally self-assured Alex Salmond to bait.
Some commentators, like Magnus Linklater this morning, see this as a gift to the SNP. That may be true, but it takes two to start a row and the SNP leader is not a dignified sight himself when he is in high dudgeon.
With his perpetual Liberal majority in Orkney and Shetland Carmichael is willing to risk saying the unsayable and ride nationalist opprobrium. He comes equipped with a thick hide and a weighty punch.
Also he had ambitions to be Secretary of State and the office gives him a much more public profile than the backroom fixing required as Lib Dem Chief whip.
Until now reasonableness had ruled the day. But during the conference season Willie Rennie, and Moore in less combative tones, attacked the idea of nationalism itself, as a philosophy.
Johann Lamont, in her speech to the Labour conference, also hinted at the dark roots of nationalism. David Cameron, in his conference comments on Scotland, also made an emotional plea to the Scottish heart as well as the head.
The Westminster government thinks it is trouncing the SNP in terms of the arguments over currency, economy, Nato membership and the rest. That might have a tone of complacency but the ground that the Coalition is taking the fight onto now is territory the SNP is complacent about too - patriotism, belonging and national identity.
Alistair Carmichal can be expected to take the gloves off and take the fight to the the SNP. His first comments in office say pretty much that.
On days like these politics is brutal, and I sympathise with Michael Moore who proved himself in the job. But the new Secretary of State, the ninth holder of the office since Devolution was meant to render it redundant (I think he called for it to be abolished himself) is going to create bigger waves.
Incidentally, Carmichael is the second islander in cabinet. Islay born he joins Danny Alexander, raised in Colonsay and South Uist, around the cabinet table. Look out Whitehall, the Highlanders are coming.