A great puzzle! This is a challenging puzzle but not an impossible one, so well worth persevering if you have the time. Thank you Io.

| ACROSS | ||
| 1 | TETRAGONAL | Not about to keep redtop in bluish square? (10) |
| NOT reversed (about) contains (to keep) RAG (redtop, newspaper) inside TEAL (bluish, colour) | ||
| 6 | See 25 | |
| 9 | IN ADDITION | Damage I did at party to trousers and to boot (2,8) |
| anagram (damage) of I DID AT inside (…trousers, puts in pocket) IN ON (party to) | ||
| 10, 23 | SAME HERE | Earl on edge when retiring me too! (4,4) |
| E (earl) RE (on, concerning) HEM (edge) AS (when) all reversed (retiring) | ||
| 11 | THROUGH-GOING | Energetic due to the state of course (12) |
| THROUGH (due to) and GOING (state of racecourse) | ||
| 15 | ALAMO | Mission evoking bedside manner? (5) |
| A LA (evoking) MO (modus operandi, bedside manner perhaps) – The Alamo Mission in Texas. or A LA MO (Medical Officer) | ||
| 16 | OMITTANCE | In form of containment, all but one name suffering this? (9) |
| anagram (form of) COnTAInMENT missing all but one N (name) | ||
| 17 | BIG CHEESE | For somebody with B, I’ll find two Es hard to take in GCSE (3,6) |
| B then I with (will find) then EE (two Es) following (…taken by…) H (hard) inside GCSE | ||
| 18 | NOT ON | Out in the nineties, so this impossible! (3,2) |
| NO TON (out in the nineties, so not a century) – cricket | ||
| 19 | RETURN CREASE | Deliveryman restricted by this proceeds to double up (6,6) |
| RETURN (proceeds) and CREASE (to double up) | ||
| 23 | See 10 | |
| 24 | CLOSE RANGE | Stop row, seeing eye to eye? (5-5) |
| CLOSE (stop, bring to an end) and RANGE (row) | ||
| 25, 6 | PLAYABLE | Indeed, ball moving around in games might not be! (8) |
| AY (indeed) inside (with…around) anagram (moving) of BALL all inside PE (games) – definition is an extension of the wordplay | ||
| 26 | AMPERE HOUR | Some charge a master for one – what of us? (6,4) |
| A MA (master) PER (for one) EH (what) OUR (of us) | ||
| DOWN | ||
| 1, 2, 3 | THIS THAT AND THE OTHER | Miscellany on the wagon includes his hat, it follows (4,4,3,3,5) |
| TT (on the wagon) contains HIS then HAT then AND with (..follows) THE OTHER (it, sex) | ||
| 4 | OUTDO | Top garden party! (5) |
| an OUT DO might be an outside (garden) do (party) | ||
| 5 | ALONGSIDE | This “A-Teammmmm” might get you by? (9) |
| A then LONG SIDE (teammmmm, a long team) | ||
| 7 | BRAZIL NUTS | Mad about Rio chocolate centres? (6,4) |
| someone who is BRAZIL NUTS is mad about Brazil, Rio de Janeiro perhaps | ||
| 8 | EVERGREENS | Popular people work on 1:1 cases (10) |
| ERG (unit of work) RE (on, concerning) inside (…cases) EVENS (1:1, ratio or odds) | ||
| 12, 21, 22 | GET ONES ARSE INTO GEAR | Doctor initially said: “ages to regeneration”; finally: “hurry!” (3,4,4,4,4) |
| anagram (doctor) of Said (first letter, initially) and AGES TO REGENERATION – I’m not sure where finally fits in | ||
| 13 | BARBERSHOP | Harmonising “The Betrayal of Sweeney Todd”? (10) |
| a BARBER SHOP might be the shopping (betrayal) of a barber (Sweeny Todd perhaps) | ||
| 14 | TARGET AREA | Upset at a greater range of marks (6,4) |
| anagram (upset) of AT A GREATER – a mark is a target | ||
| 16 | OPERCULUM | Covering for slit work – nude, Poirot let me think (9) |
| OP (opus, work) then hERCULe (Hercule Poirot, no outer letters so nude) and UM (let me think) | ||
| 20 | ENSUE | Result: guarantee’s run out (5) |
| ENSUrE (guarantee) missing (with…out) R (run) | ||
| 21 | See 12 | |
| 22 | See 12 | |
Indeed! It took one a long time to 12 (my last in: couldn’t quite believe the scatology) & in fact I’d given up, came looking for the blog to see the last couple, no blog yet, so went back for one last go & glad I did.
Too much genius to enumerate & lot of tortuous but perfectly fair parsing.
Thanks very much to Io & PeeDee.
By gum, he makes you work hard for your cruciverbal pleasure – but I did enjoy the battle. As Grant says so much genius in amongst the torture. I particularly liked 5d
Thanks to Io and to PeeDee
I took 15a to be A LA M.O. – “like a doctor”, i.e. having a bedside manner.
Failed to parse NOT ON. No excuse really.
Got held up by the “finally” in 12,21,22 which I still don’t get and wasn’t too sure why “bedside” was in 15a. Is it MO = “bedside manner” (as in blog) or MO = “manner” with bedside meaning it is placed next to A LA?
Not keen on 11a. The word is unusual and that meaning is hard to find. It is not in my Collins and Chambers only has it as a Scottish dialect for a scolding. Googling did give the “energetic” meaning. Maybe it’s in the OED?
Thanks to Io and PeeDee.
Andrew. We crossed. I think your explanation is much better.
Hovis @4
Chambers does have it:
“through?-going (Scot through?gaun) noun
A scolding
adjective
1. Passing through
2. Active, energetic”
To Andrew: Me, too.
I was further held up by the fact that the ‘sandwich-filling’ in evERGREens is palindromic, leaving me floundering for a non-existent reversal-indicator.
I think that the ‘initially/finally device in 12 etc is just for the balance (& confusion) of the surface: it works fine without, but who wants ‘simple’ when it’s Io?
This was a delight after the recent mauling i suffered in an Elgar.
Great clues-loved BARBERSHOP and OPERCULUM (great example of an unfamiliar word being perfectly signposted)
The long ones ere a hoot.
Thanks for blog and parsing of TETRAGONAL. And on second thoughts ALAMO is doubly clever.
Thanks JH.You rock!
I thought of A LA MO (Medical Officer ) too and was in two minds which to use in the blog. I associate “bedside manner” more with genteel civilian doctors than military practice, and the Medical Officers in civilian life attend desks in government departments rather than bedsides. In retrospect I think Medical Officer is the explanation Io had in mind.
Hovis, Chambers gives through-going as an English word, the Scots bit refers to the variant spelling throughgaun
(And to crypticsue @2):
Yes, it was both ‘tortuous’ and ‘torturous’. Couldn’t let it go. Sorry!)
Thanks Gaufrid and PeeDee. Should have read the Chambers entry more carefully. My bad.
Impossible for this foot soldier. I wonder how many who tried, failed? A thoroughly wasted hour of my life.
To Moly @13:
Chin up, Moly. This was a seriously hard puzzle for a mid-weeker. You’ll see from the above that I nearly gave up meself. Have a look and learn; this was corker!
Moly @13 After getting a smattering of answers I hit a brick wall and bailed. (I’m by no means an expert solver but I’m consistent enough to have won a Saturday prize last year.) Fortunately, I found the Qaos crossword in the Guardian to be very approachable and a good bit of fun.
16a doesn’t quite work for me, since two n’s have to be omitted.
Thanks to PeeDee and IO
1a Quite unusual to have an adjective as a DBE
15a I favour the “method” interpretation with “bedside” providing the “?”
16a Is this a new clue type? Guessable from crossers but not solvable until solved.
17a Can’t make this work. “two Es hard to take” = “hee” is Yoda on crack
24a I had the def as “eye to eye”
5d I read “this” as “alongside” as well
12 etc This idiom supposes prior dawdling – “finally” is part of the def
Thanks to both with a special “well done” to PeeDee for the parsing. I filled all the squares with the correct letters but needed help with a few of the parsings. It was certainly a stretch but I needed an excuse to sit in the afternoon sun for a while – quite a while as it turned out.
I get it now – all but one n (2 out of 3) are omitted.
We knew what sort of thing to expect when we saw Io’s name – a struggle. But we stuck at it with a lot of help from wordfiner, anagram solver and thesaurus, plus confirmation in Chambers of various guesses, and surprised ourselves by finishing – albeit in a very long time.
Favourites were BIG CHEESE and BARBERSHOP.
Thanks, Io and PeeDee.
Just when I thought I was becoming quite proficient this puzzle completely floored me. It is another level and I can only admire those who finished it.
Echoing SM@21. Just shows I have lots to learn 🙂 Spent an hour to finish 50%. Humbling.
However happy that I finished Vlad all but one 🙂
Was chuffed I cracked OPERCULUM. Just learnt of this word the other day when my son brought home a snail with a wonderful operculum. Nice to see it in a grid,
I lost my temper with this and threw it in the bin after an hour.
Now I’ve seen the answers I’m even angrier.
Sorry I forgot to thank you for the big PeeDee and to congratulate you on solving it.
*blog
Thanks Io and PeeDee
Tough !! Only had three answers after the first couple of sittings, started to make headway in the third sitting and finished off with a lot of help with any sort of electronic means in a last session. Still had not much idea with the full parsing of TETRAGONAL (know of redhead as a paper, but only remembered it after seeing the blog), IN ADDITION (just couldn’t see the IN ON bit) and BARBER SHOP (got the Sweeney Todd bit, but the ‘betray’ / SHOP bit didn’t come).
Admire this setter being able to craft clues where the nuances of the meaning of his words completely mislead one for the first, second, third, etc. look until a penny drops and you see which meaning he actually meant. THROUGHGOING and OPERCULUM were the only new terms for me.
Finished in the SE corner with CLOSE RANGE and the surprising GET ONES ARSE INTO GEAR in what was a hard but enjoyable (once it was over) crossword.
PS: Really hope that Grumpy was solving it on paper and not his iPad !! 😮