Two pairs of unclued lights are theme names. Remaining unclued lights aren’t in themselves thematic, but their unchecked letters complete a book title, and part of its sub-title, in two symmetrically placed, curving lines reading down. Both phrases are (14, three words) and need highlighting. The ODE confirms 19, 28, and 43.
 

Across

6    Gathering in dry, small clothes (7, hyphened)
12    Mythic king playing darts in Oz (8)
13    Heard fuel’s powder (4)
14    Metal with odd poison (6)
16    Repair men cut rasp — they affix handles (6)
18    Milliner’s note about poet (7)
19    Not sticking in force, joining police (8)
28    Polish pal about to keep a tattoo (7, hyphened)
31    Distance from capital, jolly French island (7, two words)
33    Sea lord’s criminal trials (7)
35    Garble online poem (4)
39    I will admit a love for animal (8, two words)
41    Workshop that is blocking later working (7)
46    Add pretty cover, say, in German paper (6)
47    Like faceless god’s self-origination (6)
48    See hot meat (4)
49    Squiggly line’s dirty colour (8, two words)
50    Enslave knight halter roughly binds (7)
51    Passes church maintained by old journos (7)
 

Down

1    Fellow, one being brave (4)
2    Come from Arabian tug (6)
3    Climbing, I cool down, clutching a canteen (5)
4    Pair’s time off (4)
5    Sweden’s dark or bright (6)
8    Coloured and cut, we hear (4)
9    Composer into martinis sorry for throwing up (7)
10    The more distant church roof (6)
11    Smooth quality of boats over headland (9)
15    Writer’s career to end (7)
17    Weary, posh bores aroused 9 (5)
20    Nets round deserted weirs (6)
21    A store’s fresh oysters (6)
23    Watch’s tenth part? (5)
24    Stewed clam and bream that may be stuffed (9)
27    Nasty man cuts skins (7)
30    Ex-PM’s up for rest (5)
32    Dish’s underdone part (7)
36    Edward’s female undies (6)
37    Star’s English material (6)
40    Most of ancient city’s money (5)
42    Russian soldier returns gold (4)
43    Some ache in arm? Ow! (4)
45    Votes are agreed (4)
 
A first prize of £30 for the first correct solution opened on 30 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 2292, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.