Book to start early, before ten. Do return with us (6)
I believe the answer is:
exodus
'book' is the definition.
(I've seen this before)
'start early before ten do return with us' is the wordplay.
'start' suggests taking the first letters.
'before' is a charade indicator (letters next to each other).
'ten' becomes 'x' (roman numeral).
'return' is a reversal indicator.
'with' says to put letters next to each other.
The first letter of 'early' is 'e'.
'do' written backwards gives 'od'.
'e'+'x'+'od'+'us'='EXODUS'
'to' is the link.
(Other definitions for exodus that I've seen before include "A mass departure of people, as in Bible" , "A mass departure, as in 2nd book of Old Testament" , "sequel to first one" , "OT book - flight" , "Second book of the Old Testament" .)