Minor actor that's listed in the book along with 1D? (5)
I believe the answer is:
extra
'minor actor' is the definition.
(as in film extras)
I can't explain the remainder of the clue.
(Other definitions for extra that I've seen before include "Bit player in film" , "Additional, more than expected" , "particularly" , "fortuitous run" , "lesser player" .)