LOI was 19ac, where I was thinking “sexy” rather than “stolen”. Second last was 2dn, where I don’t know quite how to categorise the definition. Clues like 24ac had me hesitating to write the answer in when I saw it, until I had all the checkers. The wordplay in 18dn also rates a mention for being particularly obscure. Thanks to the setter for a very enjoyable puzzle!
Clues are in blue, with definitions underlined. Answers are in BOLD CAPS, then wordplay. (ABC*) means 'anagram of ABC'. Deletions are in [square brackets].
On edit: thanks to Phil Jordan for pointing out the floral Nina at 3dn+21dn, and 6dn+18dn. See the first comment!
1 Morally corrupt equivalent of ten depressions? (8)
DECADENT: count these depressions with me: mono-dent, duo-dent, … deca-dent.
5 Result of laying hold firmly (6)
CLUTCH: double definition, to do with eggs or grasping.
10 Drunk again, ale’s numbing pain (9)
ANALGESIA: “drunk” (anagram) of (AGAIN ALES*).
11 Key discussion curtailed after six (5)
VITAL: VI (six), TAL[k] “curtailed”.
12 Seconds from parching, planters use borehole as well (4)
ALSO: an answer spelled out by the second letter of each word.
13 Field expertise reduced amount of green growth (9)
LEAFINESS: LEA (field), FINESS[e] (expertise, “reduced”).
15 Pause to rest, stopping the man endlessly busy working (10)
HESITATION: SIT (rest), “stopping” HE (the man), AT I[t] (busy, “endlessly”), ON (working). One of the clues I hesitated (yes, hesitated) to write in until I had the crossing letters to confirm that it fitted.
17 Something to drive about India without success (4)
VAIN: VAN around I for India. Definition as in, “the search was vain”.
19 Chews over new leaves — hot stuff? (4)
SWAG: SWAG=G[n]AWS (chews), “over” (i.e. backwards) and without N for new.
20 Money to protect king and knight in great urban moves? (5,5)
BREAK DANCE: BREAD (money) “protecting” K (king), and N (knight) in ACE.
22 Originally eaten in Mexico, not a thing with mostly cold filling? (9)
ENCHILADA: E (“originally” Eaten), followed by CHIL[l] (“mostly” cold) “filling” NADA (in Mexico, not a thing). And, the whole clue is the definition. Definitely, high art.
24 Told office to exclude British — for their neighbours’ funding? (4)
EURO: sounds like (“told”) BUREAU, with the sound of B for British excluded. As noted, I waited for both helpers before putting this in!
26 Literarily, it’s going to weave (5)
TWILL: ‘twill with an apostrophe being a literary contraction of “it will”.
27 Piece of meat where rest can be had in dish before main course (9)
ENTRECOTE: COT (where rest can be had) in ENTRÉE (dish before main course).
28 Deny women’s being released from old prison (6)
NEGATE: release the W from NEWGATE.
29 Being There, for which acting needs time given over to Sellers’ lead (8)
PRESENCE: PRETENCE (acting), with the T changed to an S.
1 Daughters without refinement are attractive? (4)
DRAW: D (daughters), RAW (without refinement).
2 Nurse Carol naturally enters senior partner’s practice? (6-9)
CRADLE SNATCHING: CRADLE (nurse), NATCH (naturally) in SING (carol). A particularly cryptic definition, I thought, referring to an old man perhaps (the senior partner), taking up with a young woman.
3 Tidy black-clad punk getting around to canine (8)
DOGTOOTH: DO (tidy), GOTH around TO.
4 Twangy part for musician, as always (5)
NASAL: hidden answer (indicated by “part”).
6 See that vessel where hippies got it on (4-2)
LOVE-IN: LO (see that), VEIN (vessel).
7 Month Robert worked round old queen like a natural (2,3,6,4)
TO THE MANNER BORN: anagram (“worked”) of (MONTH ROBERT*), around ANNE. I remember the Penelope Keith series To the Manor Born so well, the actual answer momentarily looked like a mis-spelling.
8 List containing lines informed gang member (5,5)
HELL’S ANGEL: HEEL (list), “containing” LL (lines) and SANG (informed).
9 Answer Scottish island charge after mounting, baseless fear (8)
PARANOIA: A (answer), IONA (island), RAP (charge, as in “beat the rap”), all reversed (“mounting”).
14 Bust in Paris, our rising British author (10)
CHESTERTON: CHEST (bust), ERTON=NOTRE (in Paris, “our”; “rising”).
16 Cut yarn number in loom (8)
THREATEN: THREA[d] (“cut” yarn), TEN (number).
18 Unemployment I should lower, ending four points up (8)
IDLENESS: I’D (I should), LE-NESS = LE-SSEN (lower), with the last four letters reversed (“points up”).
21 Shade from screen infused with exotic oil (6)
VIOLET: VET (screen) “infused with” an anagram (of (“exotic”) (OIL*).
23 Famous dancer doesn’t have heart or foot moving (5)
ASTIR: the dancer was AST[a]IR[e], trimmed as instructed.
25 Unimpressive million in advance, once (4)
MERE: M (million), ERE (in advance).