Presented by Kirsty Wark
Last Thursday's Prime Ministerial Debate dropped a depth charge into the election campaign and Nick Clegg has been feeling the reverberations in the opinion polls ever since.
So the expectations surrounding tonight's "performances" are huge. And tonight the territory for the first half of the debate is foreign policy, global affairs and defence - immediately setting the Liberal Democrats apart from the Tories and Labour on not one, but two profound strategic, and ideological policies - the war in Iraq, and Trident.
The nuclear deterrent is non-negotiable for the two bigger parties, while the Lib Dems say the cost of a "like-for-like replacement of the Trident nuclear weapons system" is too high and want to find alternatives.
Europe is another fault line in the debate which will be overall I think, a tougher, dirtier affair than last week. They're all practising hard for it (once again Alastair Campbell is playing the role of David Cameron in Gordon Brown's rehearsals).
We will have the best of the debate, top notch analysis from our Political Editor Michael Crick who'll have the instant poll results on who won, and from our Diplomatic Editor Mark Urban.
Emily will be live from Bristol with a trio of political heavyweights - David Miliband, Paddy Ashdown and William Hague.
And here, our star panel of Danny Finkelstein, Peter Hyman and Olly Grender who will have been watching with the trained eyes and ears of political insiders, will give the three men no quarter.
Justin Rowlatt will track the reaction of undecided voters with "the worm" and will be monitoring all manner of social media - which has already been in ironic overdrive today after the front page attacks on Clegg. Now everything is "#nickcleggsfault". Even Peter Mandelson came to his defence.
Steve Smith is camped out as usual on the side of the M1 gathering the comments and criticisms from his Motorway Men and Women.
A TV critic and body language expert will score the gestures and tics, and how the three men responded to the straitjacket of 76 rules... and two sketch writers will tell us how they'll be writing it up in tomorrow's newspapers.
I do hope you can join us tonight on BBC Two at 10.30 for an hour-long debate special.
Kirsty
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