NINA: The letters of the alphabet appear in alphabetical order around the edge of the grid.

ACROSS
8. <kiss> OSCULATE = (A T) inside CLOSEU(-p)*
9. <opportunity> WINDOW = WIN + "DOUGH"
10. NOSES outside I = NOISES <rackets>
11. PO + NT IF + EX = PONTIFEX <pope in Rome>
12. INCUR ABILITY = INCURABILITY <hopelessness>
16. MAN GOES = MANGOES <tropical fruit>
17. WHEEZI(-n)G* = GEE WHIZ <expression of surprise>
20. LIVE + PROTEST* + D = LIVER-SPOTTED <showing signs of age>
23. <punish> KEELHAUL = →"HEEL CALL"←
26. <Zoroastrian scriptures> AVESTA = (-h)AVE STA(-ndardised)
27. <I agree> JUST SO = O→, JOUSTS
28. FIB outside LASER* = FALSE RIB <bone in chest>

DOWN
1. <military initiative> PSYOP = SY inside POP
2. "QUIZ" + LING = QUISLING
3. <pillagers> RANSACKERS = R + (SARACENS* outside K)
4. <coastal town> SEAPORT = SEAT outside PO(-o)R
5. <double> TWIN = W inside ←NIT←
6. (NL outside CIA) after U = UNCIAL <style of writing>
7. V O + ←ET← = VOTE <franchise>
13. HERBALTEA* after B = BREATHABLE <allowing moisture to evaporate
14. <follow> TAIL = "TALE"
15. <Apulian city> BARI = BAR I
18. <surprised> WIDE-EYED = "WYE DIED"
19. <calm down> COOL OFF 🡆 LOCO*
21. <ancient stone> EOLITH = ←(O inside TILE)← + H
22. ←(C IOT S)← = STOIC <not complaining>
24. (-th)E (-an)T(-iq)U(-it)I(-es) = ETUI <case>
25. <eager> AGOG = AG outside GO