5NT before the count is 'pick-a-slam', as it is in neutral and disturbed auctions.

5NT after the count declares that we hold All Keycards including the queen of trumps and lets partner take control, with the general message to bid seven if there are undisclosed playing values.

WestNorthEastSouth
KQ1pass1passAJ762
8321NTpass2passA10
KJ83pass3passAQ1095
AK7533pass4pass10
4pass4pass
5pass5NTpass
7passpasspass
5NT says 'we have all the keycards; how about it?', and opener is happy to go along, having already declared his only weakness with 3: the empty suit (which as it happens is music to responder's ears). Note that responder could safely set diamonds with 4 as opener is known to be 2335.

5NT after a negative response to a Queen Ask has a very particular version of the All Keycards message. Since responder has denied the queen of trumps, the asker must have held it all along. So by inference the apparent Queen Ask was actually an enquiry about the feature in the Queen Ask suit. Responder can now respond again with that in mind:

WestNorthEastSouth
1pass
1pass2NTpass
3pass4pass
4pass5pass
5pass5NTpass
?
5 appeared to be a Queen Ask. But after responder denied holding it, the 5NT All Keycards bids say 'No problem, I've got it; but do you have the club feature – a void?' Responses are as to a Side-suit Ask: 6 is negative, everything else confirms the void.

NEXT: Endpiece