WARNING: Contains spoilers!!

ACROSS

1 Only fish in the sea (4) SOLE
double def.

3 Tell about fool speaking in an explosive way (10) SPUTTERING
SING (tell) around PUTTER (fool around/dawdle)

9 Slice of lemon beside impure liquid stirred less (7) LUMPIER
L(emon)-slice of word lemon + anag. Impure

11 Brass instrument behind in Asian festival (7) TRUMPET
RUMP (behind) inside TET (Asian festival)

12 Clotheshorse acquires alluring automobile accessory (3,4) FOG LAMP
FOP (clotheshorse) around GLAM (alluring)

13 Partly blame dear Jason's wife (5) MEDEA
Hidden

15 Debate topic is Johnny's boy (5) ISSUE
IS + SUE (allusion to Johnny Cash’s A Boy Named Sue)

16 Devil has hurt one guy who stopped to help (9) SAMARITAN
SATAN (devil) + MAR (hurt) + I (one)

18 Extremely conservative doctor behind duo (9) HIDEBOUND
Anag. BEHIND+DUO

21 Never announced expertise (5) NOHOW
Homophone of know-how

23 Sort of palm scarab, by the sound of it (5) BETEL
Homophone of Beetle

25 Short opera piece "a treat" I snarled (7) ARIETTA
Anag. of A+TREAT+I

27 Peg recalled about core nickname (7) EPITHET
TIE (rev.) around PITH (core)

28 Girl Scout emblem reference found in work (7) TREFOIL
TOIL (work) around REF(erence)

29 Where to see lions drink, keeping at a distance at
sanctuary (6,4) SAFARI PARK
SIP (drink) around AFAR (at a dist.) + ARK (sanctuary)

30 Version of poker, boss (4) STUD
Double def.

DOWN

1 Crazy fool interrupts petty 1927 aviation feat (4,6) SOLO FLIGHT
Anag of FOOL inside SLIGHT (petty)

2 French ceramics turn up among fruit trees (7) LIMOGES
GO (turn rev.) inside LIMES (fruit trees)

4 In French city, father raised us together (4,5) PARI PASSU
PARIS (French City) around [PA (father) +US rev.)]

5 Carry male symbol (5) TOTEM
TOTE (carry) + M(ale)

6 Gold turned up in strange decor somewhere in South America (7) ECUADOR
AU (gold rev.) inside anag. of DECOR

7 Fix bug after brat left (7) IMPLANT
ANT (bug) after IMP (brat) + L(eft)

8 Teutonic invader became husband (4) GOTH
GOT (became) + H(usband)

10 I'm a General Electric icon (5) IMAGE
IM+A+GE

14 Askew and Boswell grew (10) SNOWBALLED
Anag. AND+BOSWELL

17 Concern about a date with hot party host (3,6) MAD HATTER
MATTER (concern) around A+D(ate)+H(ot)

19 Fed up about cheese interview (7) DEBRIEF
FED (rev.) around BRIE (cheese)

20 Meat seller having a more masculine appearance (7) BUTCHER
Double def.

21 Easily duped Perrier rival from the south (5) NAÏVE
Reversal of EVIAN

22 Have a good laugh about frequently withdrawn prank (7) HOTFOOT
HOOT (good laugh) around OFT (rev.)

24 Illuminated tulip adapted (3,2) LIT UP
Anag. TULIP

26 Heard twit brewed beverages (4) TEAS
Homophone of TEASE