Unclued lights are connected to a theme word (which does not appear), three in each of three different senses. Two clued lights form an anagram of a name associated with the theme and should be highlighted.
 

Across

8    Gulls escape through a hedge (4)
12    Manager almost cut American scientist (10)
13    Remove stain from tyrant? (6)
15    Nurse holds nail oddly in left hand (8)
18    Revolver on table, inactive at first, put us in hospital (9, two words)
19    Grim sabre wounded something in whale (9)
20    Appeared in incomplete small role (4)
21    Enemy crosses lake, a sheet of ice (4)
24    Soldier beat a gypsy (6)
27   ...