The unclued lights are connected by 33/23. One pair of unclued lights gives one context, in which two further pairs of unclued lights are followers of 33/23; remaining unclued lights, in another sense, are 33/23’s predecessors.
 

Across

1    Nasty offer about shock treatment for responsive organ (8)
8    Rubber — a lump’s returned (4)
11    Rarer Islamic itinerant message-bringers (12, hyphened)
12    It leaves soldiers with white marks (5)
14    Final, long ending shows addition to bill (7)
16    Greek maiden’s torment on earth (5)
17    Eddy in Glasgow is to go left (4)
22    Artist’s manipulated a ruler (8)
24    Chaos in bit of spring border (6)
25    Scot’s moment, tense,...