ACROSS
 8. <friendly> WARM = M after WAR
 9. <impossible to prevent> INEXORABLE = (EXILE BARON)*
10. <Dutch people> HOLLANDERS = LANDERS inside HOLS
11. SEC outside P = SPEC <set of features>
12. <Babylonian goddess> ISHTAR = IS H TAR
14. USB inside HANDS = HUSBANDS <married couple?>
17. (RED GIANTS SCORCH)* = SCHRODINGER'S CAT <example, in physics>
20. <capital city> KINGSTON = (.c)KING STON(e.)
22. MANIA outside _L = MANILA <material in folders>
23. EAR + _L = EARL <title>
25. MINUTIAE* inside HS = HUMANITIES <history and similar classes>
27. <the past> YESTERYEAR = YES + (RYE inside TEAR)
28. <sex party> ORGY = PORGY - P

DOWN
 1. ←_O_ TAN← = NATO <alliance>
 2. AMULET* OR = EMULATOR <one that matches>
 3. ←RENEW← outside I = WIENER <hotdog sausage>
 4. <what to call> TELEPHONE NUMBER = (NOBLEMEN UP THERE)*
 5. <klutz's exclamation> OOPS = L off ←SPOOL←
 6. <queasy feeling> NAUSEA = _N AU SEAM - M
 7. <fruit> SLOE = "SLOW"
13. <Black Sea resort> SOCHI = SO CHIC - C
15. <Haggard ruler> SHE = SH E
16. DRAW L = DRAWL <a manner of speaking>
18. <point> DOT = ←TO D←
19. <authority> SANCTION = CONTAINS*
21. GO outside ←TALE← = GELATO <dessert>
22. ANT inside ←ARM← = MANTRA <repeated motto>
24. <Olympian> ARES = A_ R_ E_ S_
25. [-s]HARP = HARP <string instrument>
26. ERG O = ERGO <so>