Two unclued lights form a three-word phrase. Clues in italics are cryptic indications of partial answers; in each case, the indicated part must do as instructed by the thematic phrase to create the full answer to be entered in the grid. Resulting entries (two of which consist of two words each) are defined by unclued lights.
 

Across

9    Unravelling clue, I found measure of capacity (10, two words)
11    Old smuggler in hat offloading barrels (5)
12    Left capital protected by great force, going west in boat (7)
14    Singular brilliant spire (5)
16    Florid colour reflected in precious metal (6)
21    Calm in the morning aboard shallow vessel (8)
22    Item for fishing in Scotland, favourite around remote north (7, two words)
24    Knight errant one found in element (4)
25    Island united for demigod (4)
28    Troy? Ruined realm in end (8)
34    Bundle in past split by stick? Not good (5)
35    Earl delayed cheer (5)
37    Clothes to wash? Note several, first off (7)
38    Slow movements from primordial entity (5)
39    Hard time, right away
40    Echo following mantra
41    Insects around pole (5)
 

Down

1    One old treaty, omitting chapter in book, not rejected by body (13)
3    Sour liquid raised storm indeed (6)
4    Carter’s assistant and agent pitch up (6)
5    Bitterness in club without women (4)
6    Exhibition’s opening
7 Windows in small chambers lacking length (5)
8    Pearly king entering on cue as arranged (8)
10   Fabric seen at night is different (13, two words)
13   Centre of trade
15    Bring forward stage in festival (6)
17    Real gold around court above middle of wall (6)
18    Improvise with strip of pasta (6)
19    Comprehensive point at heart of sport brought up (7)
23    Love poet nearly smothered (8)
26    Dislike doffing hat
29    System joined with trough (6)
30    Arrival, see, in port on time (6)
31    Learn about decay in tropical plant (6)
32    General course for singer (5)
36    Long almanac helpful to some extent (4)
 
A first prize of £30 for the first correct solution opened on 30 April. 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 2354, The Spectator, 22 Old Queen Street, London SW1H 9HP. Please allow six weeks for prize delivery.