After a week in which the three political leaders have found themselves in uncharted territory, Messrs Brown, Cameron and Clegg return tonight to stir the pot in Sky's debate on foreign affairs.
The main problem they face is trying to catch the drift of a public mood, which even the public don't understand. This election, as has been noted, is a "hovering pencil" poll. Come 6 May, hundreds of thousands of voters will stand over their ballot paper, scratch their heads and wonder which box to tick.
When there is such volatility, even skilled political operators can find themselves swept away by an unexpected gust of public feeling.
Mr Cameron caught the full blast last week, when Mr Clegg stole his mantle as the "change" candidate of choice. Somehow this evening, he must grasp the initiative back. The danger is that he overreacts to the public's overreaction. An all-out assault on the Lib Dem leader might end up looking panicky. And while his reserved approach of last week didn't work, this week it might. It would be far better for Mr Cameron to simply stay the course he set last week, and hope that his policies and his values come through.
For Mr Clegg, the danger is the pressure of expectation. Having been compared to both Barack Obama and Winston Churchill over the past few days, the scene is perfectly set for Britain's new political star to come crashing to the floor. But he will be hopeful that his party's populist policies on Iraq and Afghanistan once again prove his point that he is the election's distinctive voice.
That leaves Mr Brown. It has been a weird week for the Prime Minister. Thanks to the Lib Dem surge, his poll ratings now put him below Michael Foot. But, also thanks to the Lib Dems, he is on course to win most seats. Mr Brown can be expected to continue his tactics of last week; attacks on Mr Cameron and a love-in with Mr Clegg. But his advisers must stop him saying "I agree with Nick", as he did seven times last week. If it is uttered even once tonight, he may be lampooned out of the race.