Romeo appears in simple book's outline (5)
I believe the answer is:
draft
'book's outline' is the definition.
(I've seen this before)
'romeo appears in simple' is the wordplay.
'romeo' becomes 'r' (phonetic alphabet: alpha, bravo, charlie etc.).
'appears in' means one lot of letters goes inside another.
'simple' becomes 'daft' (I've seen this in another clue).
'r' going within 'daft' is 'DRAFT'.
(Other definitions for draft that I've seen before include "conscript" , "Preliminary drawing" , "Preliminary text or plan" , "Provisional document" , "Written plan" .)