One making a promise in page introducing book (7)
I believe the answer is:
pledger
'one making a promise' is the definition.
The definition suggests a singular noun which matches the answer.
'page introducing book' is the wordplay.
I cannot really understand how this works, but
'page' could be 'p' and 'p' is found in the answer.
'book' could be 'ledger' (synonyms) and 'ledger' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for pledger that I've seen before include "One promising" , "Promising person" , "He promises" , "He commits" .)