No 11921, Friday 03 Feb 2017, Anon

ACROSS
1   Grant immunity to former secretary from beginning to end (6) EXEMPT {EX}{(-t)EMP(+t)T}
4   Understands market index almost with final lessons (6) SENSES {SENSEx}{l...nS}
9   Chooses to stop at sea (4) OPTS*
10 Feint roars disquieted wet woodland (10) RAINFOREST*
11 Plant extract in Decatur nipa (6) TURNIP [T]

12 A model caring for auditor (8) ATTENDER {A}{T}{TENDER} What's the definition? See comments
13 Bill to embark on escapade (9) ADVENTURE {AD}{VENTURE}
15 Initially step in to thump animal (5) BEAST {BEA{Step}T}
16 Walks from back to front of room (5) SPACE (+s)SPACE(-s)
18 Let a broth cook at engagement (9) BETROTHAL*
22 Be put into exhibition of Eden (8) PARADISE {PARAD{IS}E}
23 Penalize press protecting Northern Ireland (6) PUNISH {PU{NI}SH}
25 Sets up academies (10) INSTITUTES [DD]
26 Fish returns from practice (4) CARP [T<=]

27 Creeps relax in ship (6) SIDLES {S{IDLE}S}
28 Fishes in southern corners (6) SNOOKS {S}{NOOKS}

DOWN
1   Analyse currency once before (7) EXPOUND {EX}{POUND}
2   Missing island, monster returns to German city (5) ESSEN NESSiE <=
3   Correspondence with a favourite guard (7) PARAPET {PARA}{PET} (Addendum - {PAR}{A}{PET} - See comments)
5   Corrupt heartless gremlin at carnival (6) EFFETE {ElF}{FETE}
6   Uncompromising patron to ring specialist (9) STRINGENT {ST}{RING}{ENT}
7   Siblings have subtle RSS ties (7) SISTERS*
8   Ratings seemed to cause arguments (13) DISAGREEMENTS*
14 Spellbound, two Englishmen shout at editor (9) ENCHANTED {ENg...n}{CHANT}{ED}
17 Laments one getting into factories (7) PLAINTS {PLA{1}NTS}
19 Lures to moor for crime, ... (5,2) ROPES IN {ROPE}{S IN}
20 ...draws into sailors’ circles (7) ABSORBS {ABS}{ORBS}
21 Shred last document in office (6) TITTLE {d...nT} in {TITLE}
24 Cognac holder has chip (5) NACHO [T]

GRID