ACROSS
 9. GO inside ANY = AGONY <suffering>
10. <bishop> PATRIARCH = P ATRIA + RC H
11. <check out> INSPECT = (.f)IN'S PECT(o.)
12. <e.g. a> ARTICLE = ARTIC L _E
13. MO + ER inside NASTY = MONASTERY <religious building>
15. <eschew> AVOID = AV + O ID
17. JACK (GENUS + SPAIN'S)* = JACKASS PENGUINS <flightless birds>
20. _R _E _N _A + _L = RENAL <of an organ>
21. ←H CAT← inside MOUSE = MOUSTACHE <facial hair>
23. <claim> PURPORT = ←UP← R + PORT
24. <maybe> PERHAPS = PER HAS outside P
26. (YES RESIGN)* = SYNERGISE <work together>
27. <stab> SPEAR = _E inside SPAR

DOWN
 1. (.i)CANISM: A JOR(d.) = CANIS MAJOR <group of stars>
 2. CO USIN[-g] = COUSIN <family member>
 3. "TIRE" = TYRE <Levantine city-state>
 4. <untarnished> SPOTLESS = SPOT + LESS
 5. DATES* + Y = STEADY <boyfriend?>
 6. DRAUGHT outside I S T = DISTRAUGHT <shaken>
 7. BRO + ↺COLIC↺ = BROCCOLI <greens>
 8. <obsolete object> THEE = T_H + EE
14. S HH ⇒ SMALL HOURS <night time>
16. <shop> DISPENSARY = S_ PENS inside DIARY
18. <defy> CONFRONT = CON FRONT
19. E QUIPPED = EQUIPPED <given set-up>
21. <presentation of data> MATRIX = "MAY TRICKS"
22. <raw> CHAFED = FE inside CHAD
23. PA'S S = PASS <attempt at flirting>
25. <stalk> RUSH <attack without warning>