Ah, now I found it - it's the Feast of St Hilarius and St Felix ("ominous names"!
) in
Farmer Giles of Ham. Everyone, including the king and his court, was there, but the guest of honour didn't show up - the dragon!
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'Mercy!' cried Gandalf. 'If the giving of information is to be the cure of your inquisitiveness, I shall spend all the rest of my days in answering you. What more do you want to know?' 'The whole history of Middle-earth..
.'