Fraud detective tails out of a restaurant (6)
I believe the answer is:
scampi
'of a restaurant' is the definition.
The definition suggests a singular noun which matches the answer.
'fraud detective tails' is the wordplay.
'fraud' becomes 'scam' (scam is a kind of fraud).
'detective' becomes 'pi' (private investigator).
'tails' says to put letters next to each other (tail can mean to follow).
'scam'+'pi'='SCAMPI'
'out' acts as a link.
Can you help me to learn more?
(Other definitions for scampi that I've seen before include "Large prawns as food" , "Cooked Norway lobster" , "Dish of crustaceans" , "Dish of fried shrimp or prawns" , "Large sauteed prawns" .)