Across:
1 Gear (TACKLE) that’s essential for a cast (fishing TACKLE),
4 Incidents (EPISODES) of nasty (= anagram indicator) spies (spies = EPIS-S) hiding most of (c) the code (‘code’ without ‘c’ = -ODE) (EPISODES),
9 Rubs up the wrong way (ANNOYS) to lay hands on missing dhal (‘lay hands on’ missing/without ‘dhal’ = aynson = ANNOYS),
10 Detain my (detain my = DYNAMITE) butcher (= anagram indicator) – the one with the short fuse perhaps (DYNAMITE),
12 Be suspicious about (SMELL A RAT) small rate (small rate = SMELL A RAT) change (= anagram indicator),
13 Some adult relations (some ‘adult relations’ = trela = ALERT) go back (= reversal indicator) on their toes? (ALERT),
14 Key (music key E-) superpower (-STATE) spies (AGENTS) (ESTATE AGENTS) presumably responsible for promoting business in The Houses (ESTATE AGENTS),
18 Covers all the costs (FOOTS THE BILL) of soft (soft = FO-TS) marshal (= anagram indicator) tackling order (-O-) bringing most of them (most of ‘them’ = THE) to account (BILL) (FOOTS THE BILL),
21 Must get out of Mousetrap (take ‘must’ out of ‘Mousetrap’ = oerap = OPERA) and Madame Butterfly (Giacomo Puccini’s Madame Butterfly = OPERA),
22 Comes into (comes into = ECONOMIST) work (= anagram indicator) with an expert on financial management (ECONOMIST),
24 Holiday (“break” = “brake” = BRAKE) report (= homophone indicator) by the writer (PAD) (BRAKE PAD) will help one to slow down (BRAKE PAD),
25 It’s said a lot (MANTRA) – no pets in apartments (no ‘pets’ in ‘apartments’ = aarmnt = MANTRA),
26 Deer (S-IKA) consuming mostly (e) rubbish (‘waste’ without ‘e’ = -WAST-) (SWASTIKA) is emblematic of a bad regime in the past (SWASTIKA),
27 It’ll drive them to an early grave perhaps (HEARSE) having to deal with the late arrivals (HEARSE).
Down:
1 Rejects (= reversal indicator) whistle-blower’s (refs = -SFER) point (compass point north = -N-) on what’s in the museum (art = TRA-) (TRANSFER) to handover (TRANSFER),
2 Scot sent (scot sent = CONTESTS) off (= anagram indicator) in a number of competitions (CONTESTS),
3 Place bets (lay = -YAL) on long-shot tips (‘on longshot’ tips = ol) raised (= reversal indicator) (ol = LO-) (LOYAL) by trustworthy stable (LOYAL),
5 Be really careful (PAY ATTENTION), as a week’s wages (PAY) attracts the notice of a major employer (major employer/army = stand to ATTENTION) (PAY ATTENTION),
6 Avoid a court case (settle = SE-TTLE) involving a (-A) graduate (BA-) (SEA BATTLE) fighting the crafty types over water (SEA BATTLE),
7 Dublin (D-) flower (flower = -RIVER) (DRIVER) club (DRIVER golf club),
8 Worries about (SWEATS) what all the politicians want (seats = S-EATS) around Waterford (-W-) (SWEATS),
11 Hit the jackpot (BREAK THE BANK) with short holiday (BREAK) beside The Lee (THE BANK of the River Lee) (BREAK THE BANK),
15 How did one get elected (TOOK A SEAT) when one didn’t stand? (TOOK A SEAT),
16 Sister in (sister in = SINISTER) dress (= anagram indicator) that’s black (SINISTER),
17 Likes to share (FLATMATE) with novice (learner = -L-) consumed by stout (F-AT-) and Bud? (-MATE) (FLATMATE),
19 Shed tears over (sob = -BOS) unending (k) ridicule (‘mock’ without ‘k’ = moc) going all the way back (= reversal indicator) (moc = COM-) (COMBOS) to jazz bands (COMBOS),
20 Daniel (Dan = N-DA) upset (= anagram indicator) over Eva (-EVA-) (NEVADA) in precious state? (NEVADA mines gold),
23 Order (O-) from judge (-RATE) (ORATE) to speak up (ORATE).