Hi (or should that be high?) everybody.
The preamble:
In the context of the puzzle’s theme, the top and bottom lines (three and four words respectively) appear logical, but the central column (two words) disproves this; four affected characters appear as further unclued entries. Unchecked/mutually checked letters in all these might give REPENT ABYSMAL INNUENDO. When the grid is complete, solvers must FIND THE TITLE by changing an appropriately placed entry (to be highlighted), always leaving real words. Chambers Dictionary (2016) is recommended; one answer is an abbreviation.
With a few to go in the NE I nearly gave in to the temptation to look ahead, but pressed on to get all the clued answers in place before looking at the end game. (I particularly like doing this when blogging as it means I can get that part of the blog finished first.) The unclued entries were still not giving much away so I turned to REPENT ABYSMAL INNUENDO.
I had wondered if “affected” characters meant they were not entered normally into the grid, but the fact that real words would be left with only one entry changed reassured me that this was unlikely and that the characters would be affected in some other sense.
After some shuffling of the given letters (and the word counts helping too) I finally arrived at the top and bottom lines, and the central column:
GROUNDED IF MAD
SANE TO STAY PUT
EVERYBODY FLIES
and the four characters:
SNOWDEN, NATELY, DOBBS, and HUPLE
from CATCH-22 …
… which indexed the entry to change in the grid: REACT to CATCH – 22 – leaving real words, as required.
Great – thanks Gaston!

| Clue No | ANSWER | Clue with definition underlined |
| Explanation, with quoted indicators in italics and ANSWER letters in bold caps | ||
| Across | ||
| 8a | REDDLE | Ochre removing front of pedal (6) |
| We are taking the first letter from (removing front of) tREDDLE (pedal) | ||
| 9a | VAQUERO | Quaver alarmingly before old herdsman in El Paso (7) |
| QUAVER anagrammed (alarmingly) + O (old) | ||
| 11a | REHAB | Retiring swimmer hasn’t time for brief recovery (5) |
| Reversing (retiring) BA[t]HER (swimmer) hasn’t T (time) | ||
| 13a | TEASE | Tantalise supporters, we hear (5) |
| TEES (supporters), homophone (we hear) | ||
| 15a | ATOLLS | Like collecting tax for islands (6) |
| AS (like) around (collecting) TOLL (tax) | ||
| 16a | ITCH | Endlessly malicious desire (4) |
| Without external letters (endlessly), bITCHy (malicious) | ||
| 17a | WORTHIES | Unnaturally sore with deserving people (8) |
| An anagram of (unnaturally) SORE WITH | ||
| 20a | ESSAY | Empty excuses, perhaps, for tentative effort (5) |
| Empty ExcuseS + SAY (perhaps) | ||
| 22a | REACT | Concerning performance makes us respond (5) |
| RE (concerning) + ACT (performance) | ||
| 24a | RED WINES | Old stories involving success and alcoholic drinks! (8, two words) |
| REDES (old stories) containing (involving) WIN (success) | ||
| 28a | TAHA | Weaver turning back a cover (4) |
| In reverse (turning back) A and HAT (cover) | ||
| 29a | BREHON | Old Irish judge reviewing absence of plant (6) |
| Reversal of (reviewing) NO HERB (absence of plant) | ||
| 30a | FAVELA | For the young, most popular Latin American part of Rio (6) |
| FAVE (for the young, most popular) + L (Latin) + A (American) | ||
| 32a | ELITE | The best rock has no piano (5) |
| [p]ELITE (rock) has no P (piano) | ||
| 34a | LIMPS | Drags oneself forward to smother maiden with kisses (5) |
| Surround (smother) M (maiden) with LIPS (kisses) | ||
| 35a | TIE LINE | Restraint policy that’s used for private telephonic exchanges (7, two words) |
| TIE (restraint) + LINE (policy) | ||
| 36a | ACOLYTE | Faithful follower consumed bird inside (7) |
| ATE (consumed) with COLY (bird) inside | ||
| 37a | PILLAU | Tiresome person with gold dish from India (6) |
| PILL (tiresome person) + AU (gold) | ||
| Down | ||
| 1d | GRITTIER | More determined international hiding in council vehicle (8) |
| I (international) hiding in GRITTER (council vehicle) | ||
| 2d | RESENTS | Is unhappy with fissures around the Home Counties (7) |
| RENTS (fissures) around SE (the Home Counties) | ||
| 3d | UDOS | Japanese plants are okay in America (4) |
| DO (are ok) in US (America) | ||
| 4d | DEDAL | Intricate agreement with director at its heart (5) |
| DEAL (agreement) with D (director) in the middle (at its heart) | ||
| 5d | DAN DARE | Comic hero produced and read (7, two words) |
| An anagram of (produced) AND READ | ||
| 6d | FUERO | One king missing from furore about Basque constitution (5) |
| One R (king) is missing from an anagram of (… about) FU[r]ORE | ||
| 7d | ARABLE | Allegorical tale missing introduction but ready for production (6) |
| pARABLE (allegorical tale) without the first letter (missing introduction) | ||
| 10d | WEENY | Small leak over city (5) |
| WEE (leak) above (over) NY (city) | ||
| 11d | RITT | In Glasgow, scratch legal document, reportedly (4) |
| WRIT (legal document), homophone (reportedly) | ||
| 12d | HOLI | Cheerful, having time off for Spring festival (4) |
| HOLI[day] (cheerful) without (having … off) DAY (time) | ||
| 14d | THAW | What made ice melt? (4) |
| WHAT anagrammed (made) | ||
| 18d | HETE | Macbeth’s old promise disheartened chief witch? (4) |
| Without inner letters (disheartened), HEcaTE (chief witch) | ||
| 19d | STAKE OUT | Closely watch interest on loan (8, two words) |
| STAKE (interest) + OUT (on loan) | ||
| 21d | ANNATTO | Fake tan, tan with ordinary orange colourant (7) |
| An anagram of (fake) TAN TAN + O (ordinary) | ||
| 22d | RAVEL | Disentangle Maurice, perhaps (5) |
| Two definitions | ||
| 23d | CHÂTEAU | Where Gaston’s pet has something to drink? (7) |
| In French (Gaston’s) CHÂT (pet) plus EAU (something to drink) | ||
| 25d | EROICA | Heather admits love for Ludwig’s work (6) |
| ERICA (heather) goes around (admits) O (love) | ||
| 26d | DEEM | Consider raising reward (4) |
| We are reversing (raising) MEED (reward) | ||
| 27d | IONS | Clubs take away particles (4) |
| I[r]ONS (clubs) with R (take) gone (away) | ||
| 29d | BOLAS | Missile that snares type of spider (5) |
| A double definition | ||
| 31d | ADEPT | Skilled acting second-in-command, briefly (5) |
| A (acting) + DEPT. (second-in-command, briefly) | ||
| 33d | LILY | Pliantly losing the girl (4) |
| LI[the]LY (pliantly) without (losing) THE | ||
Maybe it is hiding in plain sight, but when I scrolled through the blog’s answers, I didn’t see the one abbreviation mentioned in the preamble. When I solved the puzzle I did not see it either and thought I had something wrong. Thanks to Gaston and Kitty.
Isn’t REHAB the abbreviation?
I found this very satisfying to work out, especially not having read the book or known the four surnames – but I guess everyone knows the CATCH 22 concept. Many thanks both to Gaston and to Kitty.
2@quenbarrow: Yes, that must be it, although the clue says “brief recovery,” which is enough for me. I suppose I think of an abbreviation as St. or Ave. or Dr., but those are not spoken words, whereas “rehab” is common in speech. Sort of like “bye!” for goodbye in some places. Although bye would be a shortening, it would not be an example I would cite of an abbreviation. Especially in a cryptic crossword, where abbreviations get such heavy usage.
Chambers isn’t very predictable in its flagging in this area. For example, it lists rehab as an abbreviation (whence the need for the preamble comment) but sysop simply as “short for…” which I would take as licence to clue it without a flag.
I enjoyed the puzzle, having to work out the theme by pattern-matching the unclued entries rather than via the names. Impressive to spot that the unchecked letters could be put together into so few words to make a roughly relevant phrase.