Across:
1 Cuts a rough diamond perhaps (rough cut/hack = HACKER) and is investigated for online fraud (HACKER),
4 Found in the old gardener’s chest? (old gardener/Adam) (ADAM’S RIB found in his chest) It’s the makings of the first wife! (ADAM’S RIB for Eve),
9 Took care of (NURSED) sister (NURSE-) and daughter (-D) (NURSED),
10 Analyse the vulnerable (PSYCH OUT), unstable (= anagram indicator) spy (spy = PSY-) caught (-C-) taking heroin (-H-) on holiday (OUT) (PSYCH OUT),
12 Drug (SPEED) mule – the first (‘Mule’ – the first = -M-) discovered in back (= reverse indicator) bar (bar/pub = BU-P) (SPEED BUMP) with sleeping policeman (‘sleeping policeman’ = SPEED BUMP),
13 Live (DWELL) with old Penny (D-) Spring (-WELL) (DWELL),
14 A gem worn (a gem worn) out (= anagram indicator) (a gem worn = WARMONGE-) in Waterford (-RING) (WARMONGERING) is promoting serious confrontation (WARMONGERING),
18 A small word (ABBREVIATION) from USA, for example, literally speaking (USA = ABBREVIATION),
21 What’s in front (AHEAD) of a (A-) teacher? (-HEAD) (AHEAD),
22 On a cycle (HANDLEBAR), worker (hand) loses the head (h) (‘hand’ without ‘h’ = -AND-) with the French (‘the’ French = -LE-) graduate (-BA-) in Human Resources (HR = H-R) (HANDLEBAR),
24 No more (no more) trouble (= anagram indicator) (no more = ENORMO-) for you and me (-US) (ENORMOUS) – it’s mighty! (ENORMOUS),
25 Graduate (MA = M-A) carrying a (-A-) collection of good books (New Testament = -NT-) is reading (-R-) (MANTRA) a much-repeated phrase (MANTRA),
26 An issue for the HSE? (SICKNESS) One is better off without it! (SICKNESS),
27 Greek character (Greek letter = eta = -ATE) going to night spot (bed = DEB) all set-up (= reverse all indicator) (DEBATE) by Muse (muse/ponder = DEBATE).
Down:
1 They work around the clock (hands on the clock/ work around the clock = HAND-S) outside, witnessed (witnessed/saw = -SAW-) (HANDSAWS) by those handled by for The Carpenters (HANDSAWS),
2 About (re = -ER-) to contact head of FBI (head of ‘FBI’ = -F-) back (= reverse indicator) in support (carry = CAR -RY) (CAR FERRY) of The Transporter overseas (CAR FERRY),
3 Some of the Orangemen deceived (some of the ‘orangEMEN Deceived’ = EMEND) by change (change = EMEND)
5 Critical of (DISAPPROVING) spa providing (spa providing = DISAPPROVING) treatment (= anagram indicator) (spa providing = DISAPPROVING),
6 A comedian (a comedian) touring (= anagram indicator) (a comedian = MACEDONIA) in The Balkans (MACEDONIA),
7 In order to remove Don (‘in order to’ remove ‘Don’ = irerto = RIOTER) from The Mob (RIOTER),
8 Sounds like (= homophone indicator) security (‘bail’ = ‘bale’ = BA-LE) around the race (-TT- race) (BATTLE) for a marathon clash, for example (BATTLE of Marathon),
11 Flow (SURGE-) is never-ending (‘neveR’ ending = -R-) from bottom of artery (bottom of ‘arterY’ = -Y) for periods during the day (SURGE) (SURGERY HOURS) – it’s time to see a doctor if she’s open (SURGERY HOURS),
15 Most top (‘most’ top = -M-) unopened Rosés, for instance (unopened roses = buds = -BUDS-), found in sultanate (Oman = O-MAN) (OMBUDSMAN) by government investigator (OMBUDSMAN),
16 A (-A-) club (-BAT-) on square (-T- square) occupying agents (CIA = CI-A) (CIABATTA) employed by sandwich makers (CIABATTA),
17 A sincere (a sincere) adaptation (= anagram indicator) (a sincere = INCREASE) of Spiral? (spiral = INCREASE),
19 What the journalists make (PAPERS) of documentation (ID papers = PAPERS),
20 That man (HE-) from old police force (Royal Irish Constabulary = RIC = -R-IC) capturing ring (-O-) (HEROIC) is deserving of a medal (HEROIC),
23 Longs to get out of Los Angeles (‘longs’ to get out of ‘Los Angeles’ = saele = LEASE) by charter (LEASE).