All very straightforward, as one would expect from this setter, but if anything needs further explanation please just ask.
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Across
1 Understand leader of faction, in briefly (6)
FATHOM – F[action] (leader of faction) AT HOM[e] (in briefly)
4 Close deal over late drink (8)
NIGHTCAP – NIGH (close) PACT (deal) reversed (over)
9 Feel sorry about Garbo losing article? (6)
REGRET – RE (about) GRET[a] (Garbo losing article)
10 Cola: a cup ordered in famous beach resort (8)
ACAPULCO – an anagram (ordered) of COLA A CUP
12 Turmoil caused by wizard holding Latin mass (9)
MAELSTROM – MAESTRO (wizard) around (holding) L (Latin) followed by M (mass)
13 Manage to protect small thicket (5)
COPSE – COPE (manage) around (to protect) S (small)
14 Perhaps a half fire complaints off (6,8)
SIMPLE FRACTION – an anagram (off) of FIRE COMPLAINTS
17 Suspicious deaths, enthralling a politician and former PM, in part of London (9,5)
HAMPSTEAD HEATH – an anagram (suspicious) of DEATHS around (enthralling) A MP (a politician) followed by HEATH (former PM) – Sir Edward Heath
21 Soundly criticise a form of light entertainment (5)
REVUE – sounds like (soundly) ‘review’ (criticise)
22 Reptile runs by a log, tail twitching (9)
ALLIGATOR – an anagram (twitching) of A LOG TAIL followed by R (runs)
24 Model soldier, like leader of military (8)
PARADIGM – PARA (soldier) DIG (like) M[ilitary] (leader of military)
25 Picture producer, one leaving America in disguise (6)
CAMERA – an anagram (in disguise) of AMER[i]CA
26 Wandering in Lincoln, Rolls-Royce worker? (8)
ABERRANT – ABE (Lincoln) RR (Rolls-Royce) ANT (worker)
27 Conjecture made by those people hoarding gold (6)
THEORY – THEY (those people) around (hoarding) OR (gold)
Down
1 First and second in woodland (8)
FOREMOST – MO (second) in FOREST (woodland)
2 Pair of wrestlers, game couple (3,4)
TAG TEAM – TAG (game) TEAM (couple)
3 Famous American athlete turned up fresh, entering round second (5)
OWENS – NEW (fresh) reversed (turned up) in (entering) O (round) S (second) – Jesse Owens
5 Unrivalled, earnings involving short story (12)
INCOMPARABLE – INCOME (earnings) around (involving) PARABL[e] (short story)
6 Drink after social game (9)
HOPSCOTCH – SCOTCH (drink) after HOP (social)
7 Combo’s leader plays new love song (7)
CALYPSO – C[ombo] (combo’s leader) followed by an anagram (new) of PLAYS then O (love)
8 Place above for small bird (6)
PLOVER – PL (place) OVER (above)
11 Net gain? Import faring badly (6,6)
PROFIT MARGIN – an anagram (badly) of IMPORT FARING
15 I see what you’re saying (3-6)
LIP-READER – cryptic def.
16 Cleaner cautious about young man (8)
CHARLADY – CHARY (cautious) around (about) LAD (young man)
18 Unfavourable, a part of poem about duke (7)
ADVERSE – A VERSE (part of poem) around (about) D (duke)
19 Style of interior design having red coat applied (3,4)
ART DECO – an anagram (applied) of RED COAT
20 Brandy produced by good performer of popular music, reportedly (6)
GRAPPA – G (good) plus RAPPA which sounds like (reportedly) ‘rapper’ (performer of popular music)
23 Group’s first hit, top of hip-hop chart (5)
GRAPH – G[roup] (group’s first) RAP (hit) H[ip-hop] (top of hip-hop)
All these went in quickly for me. Very enjoyable.
Thanks Gaufrid and Falcon.
Record quick solve for me, I think. Nothing to frighten the horses.
Thanks to Falcon and Gaufrid. An usually quick solve for me and very enjoyable. I was only slowed down by FATHOM and MAELSTROM.
Thanks Falcon and Gaufrid
Agree that it was a pretty straightforward puzzle with a couple of minor traps – got sucked into writing INCOMPARABLY (and had to parse my way to the correct finish) and had written W—-ARY in initially at 16d which made that harder to get than it should have been.
Finished with the clever ABERRANT.