Detectives return with knowledge on singular author (7)
I believe the answer is:
dickens
'author' is the definition.
(I've seen this before)
'detectives return with knowledge on singular' is the wordplay.
'detectives' becomes 'CID' (abbreviation for Criminal Investigation Department).
'return' shows that the letters should be reversed in order.
'with' says to put letters next to each other.
'knowledge on singular' becomes 'kens' (I can't justify this - if you can you should give a lot more credence to this answer).
'cid' backwards is 'dic'.
'dic'+'kens'='DICKENS'
Can you help me to learn more?
(Other definitions for dickens that I've seen before include "Charles --, British author" , "man of note" , "British author; the Devil" , "Author of Our Mutual Friend, d. 1870" , "See 1" .)