Cryptic crossword No 492

Polymath, I approached on tiptoe, having had my hat handed to me by the remarkable #482. This was a different experience, no pushover, but certainly more accessible. There are many beauties: 12d is excellent; 21a is a sitting duck, but I have never seen it before; 28a is fun; 23d is clever; and 25a is a satisfying anagram. Overall, very satisfying and quirky. Nice work! On this occasion, I will venture a few comments that contain spoilers……