Unclued lights, all confirmed in Chambers or Collins, are three sets of four words of a kind, each set relating differently to a theme word which must be shaded in the completed grid.
 

Across

11    Religious devotee keeping a church in shade (6)
12    Sloth in tangles in New Zealand trees (6)
13    Country moving forward area for us in Jamaica (5, doubly hyphened)
17    Muppet grabbed by squirrel-monkey (4)
18    Physicist’s ally, one protecting university (5)
19    Ending operation led by twit (7)
23    Message from paperweight? (8)
24    Recent clothing still a youngster’s outfit (7)
25    A bit downcast, I jeer about fools (6)
30    Record one banal bit of verse (8)
34    Scot’s climbed in South, stripped off (7)
35    Bard’s to shut up bird and soldiers (5)
36    Obtain a shoe from Japan (4)
38    Evil-doer’s gossip during tests (7)
40    Scot’s one possessing flash car that’s fine (6)
41    Tree rings covered in acid (6)
42    Worker with ace pilaster (4)
43    Maybe flaky mash lines wok (8)
 

Down

2    Team beheaded in prison (4)
3    Old charge? Almost finished admitting it (6)
4    Young runner allowed to lap always (7)
5    Sign sent to rotate crops (10)
7    Writer’s to indulge, penning ‘Flowing Lethe’ (11)
8    Master aims to move moon of Saturn (5)
9    Decorated with wavy line and remaining diamonds (9)
10    Old lady, one writing about dwarf’s condition (6)
14    Goodness stored in no nice new antibiotic (8)
16    Small, flying bees return in underground rooms (11)
20    Mostly tough garment cut for farm workers (10)
21    Kind of mollusc vet treated without competitor (8)
27    River once more knocked over artist (7)
30    Fenland channel keeps bearing waste (6)
31    Hebrew speech mark, say, hard to put in note (6)
32    French girl in flannelette dolled up (6)
 
A first prize of £30 for the first correct solution opened on 28 January. There are two runners-up prizes of £20. (UK solvers can choose to receive the latest edition of the Chambers dictionary instead of cash — ring the word ‘dictionary’.) Entries to: Crossword 2390, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.