I did enjoy the supporting cast of this puzzle, especially poor Molly Malone, and my clue of the day does go to the clever and classical 33dn in spite of my woes. Thanks setter!
ACROSS
1 Murderer getting heartless blow in does for friar (8)
CAPUCHIN – CAIN [murderer] getting PU{n}CH [“heartless” blow] in
5 Writer, person seen in retrospect as a workhorse (6)
DOBBIN – NIB BOD [writer | person] reversed
9 Ministers as scoundrels entertaining chief troublemaker (7)
CURATES – CURS [scoundrels] “entertaining” ATE [chief troublemaker – the goddess of mischief]
14 Instrument in new parish church men installed finally (11)
HARPSICHORD – (PARISH*) [“new”] + CH OR [church | men] + {installe}D
15 Assistant in campaign supposedly organising husband? (7,4)
RUNNING MATE – RUNNING [supposedly organising] + MATE [husband]
16 Timid person not wanting B&B with a dish from India (5)
RAITA – RA{bb}IT [timid person, losing two B’s] with A
17 Brilliant grown-up not admitting daughter is a failure (7)
DEFAULT – DEF [brilliant] + A{d}ULT [grown-up, not admitting D for daughter]
18 Top model no plainer when dishevelled (9)
NONPAREIL – (NO PLAINER*) [“dishevelled”]
19 Lizard-like son, one with unorthodox beliefs about university (7)
SAURIAN – S [son] + ARIAN [one with unorthodox beliefs, cf the Arian Heresy] about U [university]
20 Actress is female beast ensnaring man at conference with bags of money (7,8)
MARLENE DIETRICH – MARE [female beast] “ensnaring” LEN [man] at DIET [conference] + RICH [with bags of money]
22 Heavenly body expert gets mapping device (5,5)
PLANE TABLE – PLANET ABLE [heavenly body | expert]. DNK “plane table”, but one’s used in surveying.
23 Sailors coming to American saint’s home city (6)
TARSUS РTARS [sailors] coming to US [American]. The saint is Paul n̩ Saul.
25 Square in town in England (4)
NINE – hidden in {tow}N IN E{ngland}. 3×3
28 Ability to mix with ordinary folk? Opposite of what Midas had? (3,6,5)
THE COMMON TOUCH – quirky double def, imagining an inverse of the touch that turned all to gold.
30 Mean chaps beginning to trash garden flat? (8)
BASEMENT – BASE MEN [mean | chaps] + T{rash}
32 Disorganised friends in retreat run (8)
SLAPDASH – PALS reversed [friends “in retreat”] + DASH [run]
34 Those who give a lift to a player who can’t keep going? (9,5)
STRETCHER PARTY – cryptic def
37 Metal one put on a type of board (4)
IRON – double def with “a thing you put on a type of (i.e. ironing) board”
38 Enclosure made of hard material sheltering rook (6)
CORRAL – CORAL [hard material] “sheltering” R [rook]
39 Think again about tricks with notion not quite right (10)
RECONSIDER – RE CONS IDE{a} R [about | tricks | notion, “not quite” | right]
43 Ten male garments repaired for members of royal household (9-2-4)
GENTLEMEN-AT-ARMS – (TEN MALE GARMENTS*) [“repaired”]
45 Finished, complete, nothing missing (7)
THROUGH – TH{o}ROUGH [complete, missing an O for nothing]
47 Land not the first to be associated with revolutionary university song (9)
ROUNDELAY – {g}ROUND [land, “not the first”] + YALE reversed [“revolutionary” university]
49 Food dish — a thing scraped endlessly after end of supper? (7)
RAVIOLI – A VIOLI{n} [a thing scraped, “endlessly”] after {suppe}R
51 Speck of dust perhaps left in commercial building (5)
MOTEL – MOTE L [speck of dust, perhaps | left]
52 Sensitive kind? Then sin is out (4-7)
THIN-SKINNED – (KIND THEN SIN*) [“out”]
53 A complaint associated with those who serve day in day out? (6,5)
TENNIS ELBOW – cryptic def, where the “serving” is of tennis balls.
54 Make a sort of error in gym, fuzzy to begin with (7)
MISTYPE – P.E. [gym], MISTY [fuzzy] to being with
55 What adds a final bit of etiquette to requests? (6)
PLEASE – {etiquett}E is added to PLEAS [request], &lit
56 This person beginning to stir, nap cut short making one most confused (8)
MESSIEST – ME [this person] + S{tir} + SIEST{a} [nap “cut short”]
DOWN
1 Groups commander leads deficient, beginning to end (7)
COHORTS – C.O. [commander] leads {S->}HORT, [deficient, with the beginning letter moved to the end]
2 Page on Express consisting of very small pieces (11)
PARTICULATE – P [page] on ARTICULATE [express]
3 Actors with words supposedly inaudible on stage may be discarded (4,5)
CAST ASIDE – CAST [actors] with ASIDE [words supposedly inaudible on stage]
4 Mini-acts include fanciful pieces for the pit orchestra maybe (10,5)
INCIDENTAL MUSIC – (MINI-ACTS INCLUDE*) [“fanciful”]
6 Fogeyish folk who may be reluctant to relinquish duties on train? (3,5)
OLD GUARD – quirky double def playing on a potential double meaning of the “guard” in OLD GUARD.
7 End hostilities but conceal evidence of murder weapon? (4,3,7)
BURY THE HATCHET – quirky double def imagining an alternative hatchet-burying scenario.
8 Sensible end to discussion one’s repeatedly engineered (2-8)
NO-NONSENSE – ({discussio}N ONE’S + {discussio}N ONE’S*) [“engineered”]
9 Drink? There’s song about one having another one (7)
CHIANTI – CHANT [song] about I [one], plus another I [one]
10 Dance music good for inclusion in newspaper article (5)
RAGGA – G [good] for inclusion in RAG [newspaper] + A [article]
11 New Inn greeted a female performer (11)
TRAGEDIENNE – (INN GREETED A*) [“new”]
12 What Bible says thou shalt not do with thy secret (8)
STEALTHY – STEAL [what Bible says thou shalt not do] with THY
13 Predator in northward run (4)
WOLF – FLOW [run] from bottom to top
14 Maiden, unaccompanied Dublin street vendor (6)
MALONE – M ALONE [maiden | unaccompanied]. Referring to Molly Malone, who sold cockles and mussels (alive, alive, oh) from her wheelbarrow on the streets of Dublin, and whose ghost may do so still.
21 Numbers quiet about European Union become uneasy (5,2)
TENSE UP – TENS P [numbers | quiet] about EU
22 Part-time soldiers in stylish compound (6)
POTASH – TA [part-time soldiers] in POSH [stylish]
24 Took risks, with the possibility of a breakthrough? (6,2,4,3)
SKATED ON THIN ICE – cryptic definition, where the breakthrough imagined is not a good, and quite possibly a freezing cold, one.
26 Study area north of river crossing maybe in game (8,6)
CONTRACT BRIDGE – CON TRACT [study | area] above BRIDGE [river crossing maybe]
27 You may be enthralled by celebrity who keeps going? (6)
STAYER – YE [you] “enthralled” by STAR [celebrity]
29 What’s to be said about unwanted noise first, say (7)
ORDINAL – ORAL [to be said] about DIN [unwanted noise]
31 Winds driving sailors into ship (6)
SCREWS – CREW [sailors] into SS [ship]
33 Note Icarus, a loony in respect of this engineering discipline? (11)
AERONAUTICS – (NOTE ICARUS A*) [“loony”]. Semi-&lit, as Icarus famously met his end due to reckless aeronautics.
35 Awe-inspiring soldiers, not to be completely trusted? (11)
REDOUBTABLE – RE [soldiers] + DOUBTABLE [not to be completely trusted]
36 Biscuit tin — talk about that trademark on top (6,4)
BRANDY SNAP – SN [tin], with YAP [talk] about that; and BRAND [trademark] above it
40 Street singer’s first to grab stranger? They may be poor musically (9)
STRUMMERS – ST [street] + S{inger} to “grab” RUMMER [stranger]. Don’t try to claim this to fans of The Clash, though!
41 A sticky substance around eastern desert plant (8)
AGERATUM – A + GUM [sticky substance] around E RAT [eastern | desert]
42 Soldiers in parts generally hidden from public view (8)
PRIVATES – double def
44 First sign of anxiety is seen in fellow, bringing discomfort (7)
MALAISE – A{nxiety} IS, seen in MALE [fellow]
46 Female joining women’s group in station is an idiot (4-3)
HALF-WIT – F [female] joining WI [women’s group] in HALT [station]
48 Good-looking little girl — coy with it (5)
DISHY – DI [little girl] + SHY [coy]
50 Confesses nothing and succeeds, disregarding one (4)
OWNS – O [nothing] + W{i}NS [succeeds, “disregarding” I for one]
Didn’t quite understand MALONE and MARLENE DIETRICH was unparsed apart from the bags of money bit, so thanks as always for a fine blog.
ONG’ARA,
KENYA.