Agent wants old books put in new container (5)
I believe the answer is:
repot
'put in new container' is the definition.
'agent wants old books' is the wordplay.
'agent' becomes 'rep' (short for representative).
'wants' means one lot of letters go next to another.
'old books' becomes 'ot' (Old Testament).
'rep'+'ot'='REPOT'
(Other definitions for repot that I've seen before include "Give room to expand" , "to fit into new container" , "plant in another location" , "transfer seedlings" , "place somewhere new to put down roots" .)