Across:
1 Undermine someone’s resistance (DISARM) by losing rag in Mardi Gras (losing ‘rag’ in ‘mardi gras’ = mdiras = DISARM),
4 Lawyer (senior counsel = SC-) and sailor (able-bodied seaman = -AB-) at hearing (= homophone indicator) refused entry (‘barred’ = ‘bard’ = -BARD) (SCABBARD) for holding a sword (holds foil/sword = SCABBARD),
9 Phonologist hasn’t got lingo (‘phonologist’ hasn’t got ‘lingo’ = phoost = PHOTOS) for shots (PHOTOS),
10 Davenport (desk) isn’t finished (k) (‘desk’ without ‘k’ = DES-) on old city’s (old city’s = Troy’s = -TROYS) (DESTROYS) ruins (DESTROYS),
12 Writing (from the 3Rs = R-) to ageist (ageist = -EGIST-A-) doctor (= anagram indicator) about resistance (-R-) to first responder (first ‘responder’ = -R) (REGISTRAR) working in a hospital (REGISTRAR),
13 Bear (KOALA bear) from Orient taken out of Lake Ontario (‘Orient’ taken out of ‘Lake Ontario’ = lakao = KOALA),
14 Trust (EXPECT-) a number of countries (nations) without capital (n) (‘nations’ without ‘n’ = -ATIONS) (EXPECTATIONS) offering people hope (EXPECTATIONS),
18 A Sancho Panza type (Sancho Panza, squire of Don Quixote = RIGHT-HAND MAN) of moral (RIGHT -) with two workers (hand + man = -HAND MAN) (RIGHT-HAND MAN),
21 One (-I) endless (l) account (‘bill’ without ‘l’ = -bil = -LIB-) for a (A-) total review (= reverse all indicator) (ALIBI) of cover story (ALIBI),
22 Relents as (relents as = ALERTNESS) travelling (= anagram indicator) in vigilant state (ALERTNESS),
24 Jerk (T-IC) about to make a mistake (-ERR-) presuming that (-IF-) (TERRIFIC) is marvellous (TERRIFIC),
25 It’s not the same (VARIED) for a diver (a diver = VARIED) all at sea (= anagram indicator),
26 Come out of hiding (RE-EMERGE) with most of (d) the grass (‘reed’ without ‘d’ = RE-E-) for get-together (-MERGE) (RE-EMERGE),
27 Screen for Gladiator (SHIELD) or The Guard (SHIELD).
Down:
1 Legal document (DE-ED) about drink (-PORT-) (DEPORTED) is thrown out (DEPORTED)
2 In a roundabout way (= reversal indicator), spring (spa = -APS) is great (-G-) for containers (pots = STOP-) (STOPGAPS), as they’re only temporary measures (STOPGAPS),
3 Off the top of my head (ROOTS), they’re embedded in the plot (ROOTS),
5 Exonerated (CLEAR-ED) over an eyesore perhaps (-SIGHT-) (CLEAR-SIGHTED) – how perceptive is that? (CLEAR-SIGHTED),
6 Conned (BE TAKEN IN) or jailed? (BE TAKEN IN),
7 Machiavellian (AMORAL) answer (A-) to the tale of the tortoise and the hare (example of -MORAL tale) (AMORAL),
8 Aids my (aids my = DISMAY) surprise (= anagram indicator) and alarm (DISMAY),
11 It’s astonishing (BREATHTAKING) cutting one’s airtime? (BREATHTAKING),
15 Judge (CRITIC-) is (-IS-) behind pilgrimage (behind/last letter of ‘pilgrimage’ = -E) (CRITICISE) to Knock at a local level (local ‘knock’ = CRITICISE),
16 Reverse (= reversal indicator) engineering (-E) by parasites (lice = -ECIL-) leads to board member inadvertently (leads to ‘Board Member Inadvertently’ = bmi = IMB-) (IMBECILE) acting foolish (IMBECILE),
17 Oscar (O-) denies (denies = -NE-SIDE-) adaptation (= anagram indicator) is primarily discriminatory (primarily/firstly ‘discriminatory’ = -D) (ONE-SIDED) or lacking in balance (ONE-SIDED),
19 Write a (write a = WAITER) novel (= anagram indicator) at the table laying out the dishy stuff from The Restaurant (WAITER),
20 Pass through (PIERCE) Clare (-CE) to open (= position indicator) a place to fish (PIER-) (PIERCE),
23 Refuse (refuse/garbage = TRASH) initial treatment (initial ‘treatment’ = T-) for reaction to poison ivy (-RASH) (TRASH).