No 13660, Wednesday 14 Sep 2022, Vidwan

Solution to 20D has been deliberately left unsolved and is to be answered only by a non-regular / novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.

ACROSS

1   Almost 'sleepless' city (6) NAPLES NAPLESs

5   First point made in an open court perhaps (7) FIFTEEN [CD]

10 John's operating principle (5) CANON {CAN}{ON}

11 Argument results after agent gets high with this drink (3) RUM aRgUMent

12 Staff working for nobleman (5) BARON {BAR}{ON}

13 Just don't start to panic! (5) RIGHT fRIGHT

14 Getting used to run-in and meet sorts (9) INUREMENT {RUN+IN+MEET}*

15 Engagement with that trouble making, striking trade union (9) BETROTHAL {THAT+tROuBLE}*

16 Shakira's ex is hurt (5) PIQUE [DD]

18 Remdesivir usually limits this microbe (5) VIRUS [T]

19 Charm is about living in a sin as part of destiny (9) FASCINATE {F{A}{S{C}IN}ATE}

21 Reed wrung out, had come up from beneath (9) UNDERGREW*

23 Buyer wanting large piece of rock (5) CLINT CLIeNT E/Large? Something wrong here See comments

24 No-limits party lingo (5) HINDI sHINDIg

25 Basically atmosphere is route to relay (3) AIR Acrosic

26 British Royal having fresh air of a wild rose (5) BRIAR {B}{R}{AIR*} (Correction - {B}{AIR*}{R} - See comments)

27 R = Archie (3,4) RED HEAD {Red}

28 Spent days around the empty stable (6) STEADY {S{ThE}ADY*}

DOWN

2   One who gives up hate is disheartened, overcomes pessimism halfway (9) ABNEGATOR {ABh{NEGATivity}OR}

3   7 letters for years spent in office (6,2,7) LENGTH OF SERVICE (Service has 7 letters)

4   Heterosexual, progressive and uncomplicated (15) STRAIGHTFORWARD [MD] (Correction - {STRAIGHT}{FORWARD} - See comments)

5   Big claim proven wrong like Zyzzyva and Zythum (6,5,5) FAMOUS LAST WORDS [DD]

6   Brief topic about 600 feet of high speed data connection (5,5,5) FIBRE OPTIC CABLE {BRIEF+TOPIC}* CABLE 

7   Eagle may shelter here finally, around one's nest (5) EYRIE {e..lE}{maY}{s...eR}{herE} over {1}

8   Free internet not right for this girl (7) NINETTE {INTErNET}*

9   Small vehicle with a black Egyptian symbol (6) SCARAB {S}{CAR}{A}{B}

17 One field managed and led by frauds partly with competence (9) QUALIFIED {1+FIELD}*<=>{QUAcks}

18 Pass over such headless liberal (7) VOUCHER {OVER+sUCH}*

20 Trading volume at every diner (6) E?T?R? (Addendum - EATERY {E9-v+at)ATERY} - See comments)  

22 Not having energy, refused to return, had lunch (5) DINED DENIeD<=

Reference List

John = CAN, About = C, British = B, Royal = R, Right =- R, Small = S, Black = B, Volume = V, Energy = E