I now realise that my query at # 22 was well wide of the mark. I became fixated with the name known to most, if not all, of us which jumped out at me from the grid.
Still stuck on 15 across and 24 down. I think 15 across might give rise to the third missing letter, because I cannot find it anywhere else. There are fairly obvious words which will fit my grid, but I cannot parse them.