Nine unclued lights are linked in three different ways (three lights to each) to a tenth, which solvers should highlight. All may be verified in Chambers.
 

Across

 
5    Wet month unproductive (6)
10    In the open, fish got cleverly hidden (10, three words)
12    Atom bombs are nuclear without exception (6, three words)
17    Trifled foolishly? (7)
18    Request provided for a time obliquely in Scotland (7)
20    In part of swine’s face, note a drop of white (8)
25    Look round Spain for a house (3)
26    Prelates leaving a cathedral en masse? (7)
28    Second petition secures a red dress (7, hyphened)
29    Say Gabon is the source of...