ACROSS
1. POST P RAN + DIAL = POSTPRANDIAL <after lunch>
8. DEV + A NAG (R inside AI) = DEVANAGARI <script>
9. BOA outside B = BOBA <tea>
10. <South Asian> DESI = D_E_S + I
11. <one keeping single idol> HENOTHEIST = HEIST outside (NOT HE)
12. <one chucks stone> MANGONEL = MANGO _N_ _E_ _L_
14. _G _A _Y _D _A _R = GAYDAR <sense of orientation?>
15. <highest point> APOGEE = A PO "G_"
17. _T ABOUT outside RE = TABOURET <stool>
19. D ERA I'LL ←RUE← = DERAILLEUR <cyclist's gear>
21. <rubbish> GUFF G_ U_ FF
23. _D IRK = DIRK <dagger>
24. D + E MOSELLE outside I = DEMOISELLE <species of dragonfly>
25. BRIEF* R + IN GENT = BIREFRINGENT <making you see double?>

DOWN
1. <talkative> PRATING = P RATING
2. <major development> SEA-CHANGE = (..e)S EACH ANGE(l..)
3. <incognito detective> PLANCLOTHESMAN = (A MELANIN SPLOTCH)*
4. TI inside ALT = ATILT <having some pitch?>
5. <doubt> DUBIETY = B IE inside DUTY
6. <unexpected appearance> AMBUSCADE = AM BUS CA DE
7. LED E = LEDE <article's opening lines>
13. (PALE PINT I)* = APPLETINI <fruity cocktail>
14. <twill fabric> GABARDINE = (..n)G A BARD IN E(l..)
16. <singer> GRACKLE = RACK inside LEG*
18. <remedy> UNGUENT = GUN* _U_ + ENT
20. LID AR = LIDAR <device for detecting objects' position>
22. F ILK = FILK <music with a sci-fi theme>