Thanks Tees for an enjoyable puzzle. Definitions are underlined in the clues.
Across
9 Subcontract abroad before spring (9)
OUTSOURCE : OUT(abroad/out of the country) plus(before) SOURCE(a spring/a place, person, or thing from which something originates or can be obtained).
Defn: …, and often abroad.
10 Versace to be cleaned out by Scottish bank — wait and see? (5)
VERBS : “Versace” minus its inner letters(to be cleaned out) plus(by) RBS(abbrev. for the Royal Bank of Scotland).
Defn: … are examples/? of this class of words in grammar.
11 Expert playing East German college supremo (7)
PROVOST : PRO(short for “a professional”/an expert in his/her field) + V(abbrev. for “versus”/playing against in a competition) + OST(“east” in German).
12 Looked up to say more about Slough (7)
ADMIRED : ADD(to say more/expand on what you said) containing(about) MIRE(a slough/a stretch of swampy ground).
13 Fish found regularly in Trent area (5)
TETRA : 1st, 3rd, 5th, 7th, 9th letters of(found regularly in) “Trent area“.

14 Handyman who holds forth at Xmas time? (9)
DECORATOR : ORATOR(one who holds forth/gives a speech or lecture) placed after(at) DEC(abbrev. for “December”, the time of the year when Xmas happens).
16 Ministers in closet with stars (4,11)
HOME SECRETARIES : HOME(in, as in “I’ll be home for the next 14 days”) + SECRET(closet/descriptive of something undisclosed, as in “he’s a closet cross-dresser”) plus(with) ARIES(the small constellation of stars said to look like a ram).
19 Find nightclub dead (9)
DISCOVERY : DISCO(a type of nightclub popular in the 70s) + VERY(dead/absolutely, as in “you’re dead right!”).
Defn: … as a noun.
21 Spanish mate advanced with dynamism on M1 (5)
AMIGO : A(abbrev. for “advanced”) plus(with) [GO(dynamism/drive) placed after(on) MI(M1 with the Roman numeral substitution).
22 Incestuous son Opus Dei corrupted inwardly (7)
OEDIPUS : OPUS containing(… inwardly) anagram of(… corrupted) DEI.
23 Scrub computer key inside protective covering (7)
RESCIND : ESC(short for “escape” one of the keys/buttons on your computer keyboard) contained in(inside) RIND(a protective covering, as around an orange, say).
24 Capital city replacing Kyoto (5)
TOKYO : Anagram of(replacing) KYOTO.
Defn: City which replaced Kyoto as the capital city of Japan.
25 Anglo-Saxon ruler has talent to waste (9)
ATHELSTAN : Anagram of(… to waste) HAS TALENT.
Down
1 Deep snow settles more easily on such a roof (3-7)
LOW-PITCHED : Double defn: 1st: …, as applied to a voice; and 2nd: …, with its sides sloping at a shallow angle.
2 Like Titanic in reality (2,6)
AT BOTTOM : [AT BOTTOM](… of the sea, where the wreck of the SS Titanic is).
Answer: Fundamentally/at heart/in reality, as in “Some believe that people are fundamentally/at bottom/in reality good”.
3 Fur or feather stole acquired in that city (6)
BOGOTA : BOA(a fur or feather stole/women’s long scarf or shawl) containing(… in that) GOT(acquired/obtained).
4 Nasty kid runs into club (4)
BRAT : R(abbrev. for “runs” in cricket scores) contained in(into) BAT(a club/a heavy stick).
5 Sensual indulgence rued by each involved (10)
DEBAUCHERY : Anagram of(… involved) RUED BY EACH.
6 Prayer girl elevated mass with melodic piece (3,5)
AVE MARIA : Reversal of(… elevated, in a down clue) EVA(a girl’s name) + M(symbol for “mass” in physics) plus(with) ARIA(a melodic piece in an opera or oratorio).
7 Doctor right person possibly seen about infestation (3,3)
DRY ROT : DR(abbrev. for “Doctor”) + reversal of(… seen about) TORY(a person with conservative or right-leaning politics, possibly a member of the Conservative Party/a Tory).
8 Employed elderly initially in Bucks? (4)
USED : 1st letter of(… initially) “elderly” contained in(in) USD(abbrev. for “US dollars”/bucks in slang).
14 Squalid detectives set up man and woman (10)
DICKENSIAN : Reversal of(… set up, in a down clue) CID(collectively, the detectives in the Criminal Investigation Department) + KEN(a man’s name of Scottish origin) plus(and) SIAN(a woman’s name of Welsh origin).
Defn: …, like the poor social conditions portrayed in Charles Dickens’ novels.
15 Someone questioned grudge involving small lake (10)
RESPONDENT : RESENT(to grudge/to mind that someone has achieved something) containing(involving) POND(a small lake/an inland body of water surrounded by land).
Defn: In law, … as a result of a petition against him/her.
17 Sign NCO produced in Swiss town (8)
SCORPION : CORP(abbrev. for “Corporal”, one of the NCO/non-commissioned officer ranks) contained in(produced in) SION(a town in the Swiss canton of Valais).
Defn: … in the zodiac.
18 Begin to explain what yours truly did at restaurant? (8)
INITIATE : [IN IT, I ATE](statement explaining what I/yours truly did in it/at the restaurant).
20 Kudos built on university logic puzzle (6)
SUDOKU : Anagram of(… built) KUDOS placed above(on, in a down clue) U(abbrev. for “university”).
21 Archbishop one rarely missing party (6)
ANSELM : AN(article in grammar for a single/one item) + “seldom”(rarely) minus(missing) “do”(a party/social function).
Defn: The once Archbishop of Canterbury, appointed in 1093.
22 Blasphemy from goatherd (4)
OATH : Hidden in(from) “goatherd“.
23 Between two rivers, what was that industrial region? (4)
RUHR : R,R(2 x abbrev. for “river”) containing(Between …, …) UH?(exclamation expressing “what was that?”/”I don’t get it”).
Defn: … in Germany.
Needed a few aids to complete this. Didn’t know ANSELM, ATHELSTAN or TETRA (although the latter was a write-in). Failed to parse DECORATOR or LOW-PITCHED properly which is a bit embarrassing.
There’s a mistake in the blog for 15d. POND is “small lake”, the S is only from “resent”.
Thanks to Tees and scchua.
Thanks Hovis. Blog corrected. (How easily distracted one can be!).
Very enjoyable thank you Tees and scchua
Unlike Hovis, as I live in Kent, I had no problems with Anselm or Athelstan, and, as for Tetra, it is one of crosswordland’s most regularly appearing fish
Quite easy for Tees, I thought, but very enjoyable nonetheless. 22A would have worked just as well without ‘inwardly’. Thanks Tees and Scchua.
This looked as though it was going to be very gentle, but then I was held up by some not so obvious ones like HOME SECRETARIES, DICKENSIAN and my last in ANSELM. I liked the &lit TOKYO, the ‘wait and see?’ def and the way in which the ‘Deep’ def for 1d was almost hidden by the surface.
Thanks to Tees and scchua
Our exprience was very much like WordPlodder’s. We also liked USED, SCORPION, INITIATE and RUHR.
Thanks, Tees and scchua.