ACROSS
 1. QUARK outside (EST I ON + M) = QUESTION MARK <?>
 9. <rush> SCURRY = S_ + CURRY
10. ←MAG← AN outside EPL = GAME PLAN <strategy>
11. <ignore> SNUB = ←BUNS←
12. RETAILER* outside _TU_ = LITERATURE <books>
13. (.i)C HEM I SE(w.) = CHEMISE <loose dress>
15. B_ RANCH = BRANCH <subsidiary>
17. P OP outside NYU = PONY UP <pay>
18. E inside CHE RIO = CHEERIO <so long>
19. <garment> HAND-ME-DOWN = (H AND M) OWNED*
22. SAS + _S = SASS <attitude>
23. <oxidising gas> FLUORINE = IRON* inside FLUE
24. P inside CRIES = CRIPES <gosh>
25. <contest> STEEPLECHASE = STEEP LEASE outside C_ H

DOWN
 2. UNABLE outside CON SCION = UNCONSCIONABLE <outrageous>
 3. (BERRY BUSH)* = SHRUBBERY <part of garden>
 4. ←(.a)LLY DI(s.)← = IDYLL <paradise>
 5. NIGH TIE = NIGHTIE <late shift?>
 6. <impressive> ADMIRABLE = ADMIRAL outside B + E
 7. <not working> KAPUT = (K A) PUT
 8. <whimsicality> CAPRICIOUSNESS = US inside CONSPIRACIES*
14. I'M PRÉCIS + E_ = IMPRECISE <rather vague>
16. <rock band> AEROSMITH = A (MORE HITS)*
18. LOSE inside CUP = CLOSE UP <draw together>
20. D_R_O_S_S = DROSS <junk material>
21. <specialist> NICHE = H inside NICE