Published in the i newspaper on 19 September 2020.
This took me much longer than usual to solve. Usually I manage to finish the Inquisitor in a couple of days but I spent four days on this one - with a midweek break, so I hadn't quite finished by the time the next one was published. The gridfill took three days on its own but there were so many extra parts to complete that I had to devote an additional morning to them. It took me quite a while to understand all the instructions!
The theme turned out to be The Scarlet Pimpernel by Baroness Orczy. The theme for the unscrambled extra words in the sixteen special Across clues was "shades of red"; the theme for the sixteen special Down clues was "flowers"; thus the target could be seen as a member of both sets. The extra letters in the clues in the top half spelt out MARGUERITE ST JUST (the Pimpernel's wife); those in the bottom half spelt out CITIZEN CHAUVELIN (his chief adversary). Details are given below the solutions to the clues.
The letters SCARLET PIMPERNEL were contained, one by one, in the solutions to the sixteen special Across clues - all unchecked in the grid. By replacing them with the letters in SIR PERCY BLAKENEY (the Pimpernel's true identity), in the same order, one could create a new set of words in the Across lights without changing any of the Down lights. Details are given at the end.
The four possible search locations were HERE and THERE (both contained within ETHEREAL in the middle row), HEAVEN (in the top row) and HELL (in the bottom row), all appearing in the novel's well-known verse: “They seek him here, they seek him there/Those Frenchies seek him everywhere/Is he in heaven or is he in hell?/That demned elusive Pimpernel.”
Note also that "Frenchies" appears in the clue for 13ac, which could be taken as an additional indication of the theme.
Solutions to clues
Redundant words are in italics; definitions are in quotes. I could only find 14ac in a single (very obscure) source, and I couldn't work out the parsing for 30ac.
I'm not sure about the parsing of 34d; either "upset" is the definition, with YA = "indeed" and WING = "member coming out of line" (why?); or "coming out of line" is the definition, with YAW = rev. ("upset") of WAY ("indeed") and ING = "member" (why?).
Across
1. SHEA - "African plant"; E in SHA[m]; musters
5. VENDOR - "slot-machine"; V + END + OR
11. UNCATE - "hooked"; anag. of (AT + [i]N + CUE); archery
12. UNLOADS - "discharges"; U[nknow]N + LOADS; lurgy
13. PEAL - "loud sound"; rev. of (LA + EP)
14. REELER - "songbird"; R + rev. of (RE + LEE); Germanic
15. CYCLE - "period"; anag. of (CLEMENCY - MEN)
17. AREOLAE - "pigmented skin patches"; rev. of (ALOE in ERA); bicker
21. KADE - "fly"; [dunkir]K + [b]ADE[r]
23. TREE - "timber"; [s]TREE[t]; roadmen
25. PATTER - "insincere speech"; PATTER[n]; article
26. ETHEREAL - "heavenly"; E + (HER in TEAL)
28. CAIMAN - "reptile"; AIM in CAN; titanic
30. HAVE - ?
31. MEAN - "humble"; hidden in [so]ME AN[imal]; dire
33. PLAYING - "on"; A in PLYING
35. BASE - "bottom"; anag. of (BARES - R); Amorino
38. EAGLE - "standard"; BEAGLE - B
40. DRAWER - "one writing on cheque"; RAW in DER; zeros
41. WHEN - "once"; WHITEN - IT
42. MANITOU - "sacred object"; MAN + I + anag. of OUT; buyer
43. RARELY - "remarkably well"; move A in (BIZARRELY - BIZ); sincere
44. SHELLS - "cases"; H for P in SPELLS
45. GOEL - "avenger"; remove middle letters of GO[sp]EL; unceasing
Down
2. HONEY - "golden brown"; HONE + Y; uptilt
3. ENLACED - "intermeshed"; anag. of ADOLESCENT - anag. of SOT; tousle
4. APOLLO - "Olympian"; A + POLL + O; seaport
6. ENDED - "over"; anag. of [i]NDEED; misreport
7. DAILY BREAD - "work"; DAILY + homophone of BRED; jovial
8. OTHER - "remaining"; BOTHER - B; downpours
9. REBRACED - "again reinforced"; BRA in RECED[e]; measuring
10. CUPCAKE - "mad American"; (anag. of PACK) in CUE; matinees
18. RATECAP - "set financial limit on"; RAT + (rev. of ACE) + P
19. ANTRAL - "cavity's"; A + (CENTRAL - CE)
20. PERLMAN - "classical musician"; PER + (M in L[e]A[r]N[t])
22. HAEMAL - "of blood"; rev. of (LAME + A[fres]H)
24. STAVESACRE - "larkspur"; E in anag. of (SEARC[h] + VAST); hilly
27. CHOBDARS - "Indian ushers"; BD in (CH + OARS); searat
29. INGENUE - "naive girl"; move IN up in GENUINE; succour
32. EIGHTVO - "book"; [h]EIGHT + V + O; divas
34. YAWING - "upset"; YA + WING; line-up [see above for alternative parsing]
36. ARRAH - "emotional expression"; anag. of (FEATHERBRAIN - BENEFIT); complain
37. BE-ALL - "Shakespeare's future"; [h]E in BALL; sanity
39. LEONE - "African bread"; L[arg]E + ONE; leanest
Unscrambling of additional words in clues
Top half | Bottom half | |||||||
Across (reds) | ||||||||
1. MUSTERS | -> RUSSET | + M | 28. TITANIC | -> TITIAN | + C | |||
11. ARCHERY | -> CHERRY | + A | 31. DIRE | -> RED | + I | |||
12. LURGY | -> GULY | + R | 33. STRUT | -> RUST | + T | |||
14. GERMANIC | -> CARMINE | + G | 35. AMORINO | -> MAROON | + I | |||
16. UNITARY | -> TYRIAN | + U | 40. ZEROS | -> ROSE | + Z | |||
17. BICKER | -> BRICK | + E | 42. BUYER | -> RUBY | + E | |||
23. ROADMEN | -> MODENA | + R | 43. SINCERE | -> CERISE | + N | |||
25. ARTICLE | -> CLARET | + I | 45. UNCEASING | -> SANGUINE | + C | |||
Down (flowers) | ||||||||
2. UPTILT | -> TULIP | + T | 24. HILLY | -> LILY | + H | |||
3. TOUSLE | -> LOTUS | + E | 27. SEARAT | -> ASTER | + A | |||
4. SEAPORT | -> PROTEA | + S | 29. SUCCOUR | -> CROCUS | + U | |||
6. MISREPORT | -> PRIMROSE | + T | 32. DIVAS | -> SIDA | + V | |||
7. JOVIAL | -> VIOLA | + J | 34. LINE-UP | -> LUPIN | + E | |||
8. DOWNPOURS | -> SNOWDROP | + U | 36. COMPLAIN | -> CAMPION | + L | |||
9. MEASURING | -> GERANIUM | + S | 37. SANITY | -> TANSY | + I | |||
10. MATINEES | -> NEMESIA | + T | 39. LEANEST | -> TEASEL | + N |
Across solutions to be modified in final grid
I wasn't certain about the legitimacy of all the modified words, particularly ALAYING; is it an alternative spelling of ALLAYING, or intended as A-LAYING (as in "six geese a-laying")? CREE only seems to exist with a capital letter as the name of an American First Nation people.
In 17 and 40 there's a choice of two letters to change, but neither ARROLAE nor DEAWER is a word, and both changes would also involve modifying Down clues, which doesn't happen anywhere else. In 1, 42 and 43 there's no actual change to the original solution.
1. | S | -> S | SHEA | unchanged | |||||||||||||||||||
11. | C | -> I | UNCATE | -> UNIATE | |||||||||||||||||||
12. | A | -> R | UNLOADS | -> UNLORDS | |||||||||||||||||||
14. | R | -> P | REELER | -> PEELER | |||||||||||||||||||
16. | L | -> E | LYRA | -> EYRA | |||||||||||||||||||
17. | E | -> R | (first E remains unchanged) | AREOLAE | -> AREOLAR | ||||||||||||||||||
23. | T | -> C | TREE | -> CREE | |||||||||||||||||||
25. | P | -> Y | PATTER | -> YATTER | |||||||||||||||||||
28. | I | -> B | CAIMAN | -> CABMAN | |||||||||||||||||||
31. | M | -> L | MEAN | -> LEAN | |||||||||||||||||||
33. | P | -> A | PLAYING | -> ALAYING | |||||||||||||||||||
35. | E | -> K | BASE | -> BASK | |||||||||||||||||||
40. | R | -> E | (first R remains unchanged) | DRAWER | -> DRAWEE | ||||||||||||||||||
42. | N | -> N | MANITOU | unchanged | |||||||||||||||||||
43. | E | -> E | RARELY | unchanged | |||||||||||||||||||
45. | L | -> Y | GOEL | -> GOEY |