Something pub may serve fraud investigator (6)
I believe the answer is:
scampi
'something pub may serve' is the definition.
I can't tell whether this definition defines the answer.
'fraud investigator' is the wordplay.
'fraud' becomes 'scam' (scam is a kind of fraud).
'investigator' becomes 'PI' (private investigator).
'scam'+'pi'='SCAMPI'
Can you help me to learn more?
(Other definitions for scampi that I've seen before include "Breaded prawns" , "Fish dish, often in rings" , "Tasty prawns in batter" , "Edible crustaceans" , "Shellfish" .)