Agent dealing with Charlie? Derrick comes up short (4)

I believe the answer is:

narc

I'm a little stuck... Click here to teach me more about this clue!

'agent dealing with charlie?' is the definition.
(narcotics agent - charlie can mean cocaine)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for narc that I've seen before include "member of drug squad" , "One on drugs squad" , "Drugs officer" , "Agent dealing with Charlie" , "Drugs agent (US)" .)

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app