Unclued lights are three groups of three words of a kind, each group defined by the name of a different main character from a novel. The fourth main character of the novel (6, two words) must be highlighted in the completed grid.
 

Across

1    I hope gas travels in passages in US (8)
8    Firms making fruit-producing plant (4)
12    Old character about to drink fill when wine’s new (9, two words)
15    Prisoner welcomes month, one that’s boiling (7)
17    Growl resounded around (4)
18    Rope from cafeteria tables (5)
19    A journalist retains right transferred once (7)
23    Drop of port wine, red, in mixture (8)
24    I’m...