ACROSS
 8. <noise> AUDIO = AUDI O_
10. OVERT HOW outside R = OVERTHROW <coup?>
11. REAR + MED = REARMED <with new weaponry>
12. EG _G_ + ⭯DONE⭯ = EGGED ON <encouraged>
13. ←(.o)OD NOW KEAT(s.)← = TAE KWON DO <art from the East>
15. <is seaman on> CREWS = "CRUISE"
17. (MAN + SHIP AT FAMOUS)* = ISTHMUS OF PANAMA <place between two oceans>
20. GEN outside IV = GIVEN <supplied>
22. (BEAGLE + VET)* = VEGETABLE <source of vitamins>
24. F + AIRWAY = FAIRWAY <driving here?>
25. <not unusual> ROUTINE = "RUE TEEN"
27. TAURUS outside HE'S = THESAURUS <reference book>
28. _AR_ GOT = ARGOT <local vernacular>

DOWN
 1. ←RAG← ROTTING = GARROTTING <murder>
 2. <standard> NORM = (N OR M?)
 3. <wet> SODDEN = SOD + DEN
 4. <shapeshifter> _WE_ ←FLOWER←
 5. <theatricality> STAGECRAFT = STAG ←FARCE← + T
 6. BRIDE outside G = BRIDGE <card game>
 7. <riverbird> SWAN = WAS* N
 9. CITADEL* = DIALECT <a manner of speaking>
14. <Next section> WOMENSWEAR = W ←NEMO← SWEAR
16. <these may be spoken> STATEMENTS = (TESTS MEANT)*
18. <French person> SAVOYARD = S AVO YARD
19. <strolling> AMBLING = AM BLING
21. DEVIL* outside E = VEILED <hidden>
23. <ostentatious> GARISH = GAR-ISH
24. <Greek cheese> FETA = "FETTER"
26. U + ←HAT← = UTAH <D-Day landing site>