Scrupulous fellow taken in by a cruel rogue (7)
I believe the answer is:
Here is my best explanation:
'scrupulous' is the definition.
(similar in meaning)
'fellow taken in by a cruel rogue' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'taken in by' indicates putting letters inside.
'rogue' is an anagram indicator.
'acruel' anagrammed gives 'careul'.
'f' inserted into 'careul' is 'CAREFUL'.