12 across: Spot what makes calmer caller? (6)
I doubt anyone would have deciphered the wordplay before working out the answer to the direct clue, for the wordplay is truly is truly devilish and inspired: what makes calmer caller = me as le (swap me in calmer with le to get caller) = measle = spot.
17 down: Broth distributed about Russian centre, cold?! (7)
Elegantly constructed &lit clue: broth distributed about Russian centre, cold = borht about sc = borscht = broth distributed about Russian centre, cold.
24 down: Handle blow-up (4)
This isn’t the most memorable of clues, but it did get me and my crossword crew thinking DA had mixed up his sexual slang before we realised that this clue is completely clean and we were being completely dirty: blow-up = bonk-up = knob = handle.
23 down: Lift notes, possibly, on model clip sealing short machine-gun (5)
I love a clever direct clue: model clip sealing short machine-gun = make – e sealing uzi – i (we spent a lot of time thinking this could have been ak47 – 47) = muzak = lift notes, possibly.
9 across: Humbert’s girl skipped it with a youngter’s cackle (3)
A little too easy because of the reference to a very fine piece of literature, but a nicely constructed clue nonetheless: Humbert’s girl skipped it with a = lolita – it – a = lol = a youngster’s cackle.
4 down: Magazines’ text about bullfighter close to Franco (10)
Concatenated words are always the hardest to guess from cross clues, and there a surprising number of synonyms for bullfighter (torero, matador, toreador), all of which made this elegant clue especially difficult to solve: text about bullfighter close to Franco = sms about torero o = storerooms = magazines.
16 across, 13 down: Mark, indulging in S/M, before beer mint (5, 8, 3)
A clue for the kinky: mark, indulging in S/M, before beer = brand spanking new = mint.