Highly valued first of trilogy certain to be found in study (9)

I believe the answer is:
treasured
'highly valued' is the definition.
'treasured' can be an answer for 'valued' (I've seen this before). I am not sure about the 'highly' bit.
'first of trilogy certain to be found in study' is the wordplay.
'first of trilogy' becomes 't' (1st letter of 'trilogy').
'certain' becomes 'sure' (synonyms).
'to be found in' means one lot of letters goes inside another.
'study' becomes 'read' (synonyms).
'sure' going inside 'read' is 'reasured'.
't'+'reasured'='TREASURED'
Can you help me to learn more?
(Other definitions for treasured that I've seen before include "Regarded as precious" , "Prized, precious" , "Cherished, held dear" , "Valuable" , "Loved" .)
