Deeply involved with taking rook in opener (5)
I believe the answer is:
intro
'rook in opener' is the definition.
'intro' can be an answer for 'opener' (I've seen this before). I am unsure of the 'rook in' bit.
'deeply involved with taking' is the wordplay.
'deeply' becomes 'r' (I can't justify this - if you can you should give a lot more credence to this answer).
'involved with' becomes 'into' (I've seen this before).
'taking' indicates putting letters inside.
'r' going into 'into' is 'INTRO'.
Can you help me to learn more?
(Other definitions for intro that I've seen before include "Opening bars to a piece of popular music" , "Opening notes" , "One starts" , "Lead-in" , "First bars of a musical composition" .)