Scrupulous fellow taken in by a cruel rogue (7)
I believe the answer is:
careful
'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.
'a'+'cruel'='acruel'
'acruel' anagrammed gives 'careul'.
'f' inserted into 'careul' is 'CAREFUL'.
(Other definitions for careful that I've seen before include "'Prudent, cautious (7)'" , "Diligent" , "Exercising caution" , "Thrifty" , "Tight-fisted" .)